From 3bc14098d8fb05b98e01c4abd901f77b55d19331 Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Fri, 20 Sep 2019 17:42:07 -0400
Subject: [PATCH 1/7] genboardscfg.py: Convert to Python 3

Convert this tool to requiring Python 3.  The bulk of this is done with
the 2to3 tool In addition, we need to use the '//' operator to have our
division result return an int rather than a float and ensure that we use
UTF-8 when reading/writing files.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
---
 tools/genboardscfg.py | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index e9bbd15e15..e9a9c11865 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0+
 #
 # Author: Masahiro Yamada <yamada.m@jp.panasonic.com>
@@ -91,7 +91,7 @@ def output_is_new(output):
 
     # Detect a board that has been removed since the current board database
     # was generated
-    with open(output) as f:
+    with open(output, encoding="utf-8") as f:
         for line in f:
             if line[0] == '#' or line == '\n':
                 continue
@@ -168,7 +168,7 @@ class KconfigScanner:
         warnings = self._conf.load_config(self._tmpfile)
         if warnings:
             for warning in warnings:
-                print '%s: %s' % (defconfig, warning)
+                print('%s: %s' % (defconfig, warning))
 
         try_remove(self._tmpfile)
         self._tmpfile = None
@@ -177,7 +177,7 @@ class KconfigScanner:
 
         # Get the value of CONFIG_SYS_ARCH, CONFIG_SYS_CPU, ... etc.
         # Set '-' if the value is empty.
-        for key, symbol in self._SYMBOL_TABLE.items():
+        for key, symbol in list(self._SYMBOL_TABLE.items()):
             value = self._conf.get_symbol(symbol).get_value()
             if value:
                 params[key] = value
@@ -242,8 +242,8 @@ def scan_defconfigs(jobs=1):
     processes = []
     queues = []
     for i in range(jobs):
-        defconfigs = all_defconfigs[total_boards * i / jobs :
-                                    total_boards * (i + 1) / jobs]
+        defconfigs = all_defconfigs[total_boards * i // jobs :
+                                    total_boards * (i + 1) // jobs]
         q = multiprocessing.Queue(maxsize=-1)
         p = multiprocessing.Process(target=scan_defconfigs_for_multiprocess,
                                     args=(q, defconfigs))
@@ -290,7 +290,7 @@ class MaintainersDatabase:
           'Active', 'Orphan' or '-'.
         """
         if not target in self.database:
-            print >> sys.stderr, "WARNING: no status info for '%s'" % target
+            print("WARNING: no status info for '%s'" % target, file=sys.stderr)
             return '-'
 
         tmp = self.database[target][0]
@@ -301,8 +301,8 @@ class MaintainersDatabase:
         elif tmp.startswith('Orphan'):
             return 'Orphan'
         else:
-            print >> sys.stderr, ("WARNING: %s: unknown status for '%s'" %
-                                  (tmp, target))
+            print(("WARNING: %s: unknown status for '%s'" %
+                                  (tmp, target)), file=sys.stderr)
             return '-'
 
     def get_maintainers(self, target):
@@ -313,7 +313,7 @@ class MaintainersDatabase:
           they are separated with colons.
         """
         if not target in self.database:
-            print >> sys.stderr, "WARNING: no maintainers for '%s'" % target
+            print("WARNING: no maintainers for '%s'" % target, file=sys.stderr)
             return ''
 
         return ':'.join(self.database[target][1])
@@ -330,7 +330,7 @@ class MaintainersDatabase:
         targets = []
         maintainers = []
         status = '-'
-        for line in open(file):
+        for line in open(file, encoding="utf-8"):
             # Check also commented maintainers
             if line[:3] == '#M:':
                 line = line[1:]
@@ -404,7 +404,7 @@ def format_and_output(params_list, output):
     # ignore case when sorting
     output_lines.sort(key=str.lower)
 
-    with open(output, 'w') as f:
+    with open(output, 'w', encoding="utf-8") as f:
         f.write(COMMENT_BLOCK + '\n'.join(output_lines) + '\n')
 
 def gen_boards_cfg(output, jobs=1, force=False):
@@ -418,7 +418,7 @@ def gen_boards_cfg(output, jobs=1, force=False):
     check_top_directory()
 
     if not force and output_is_new(output):
-        print "%s is up to date. Nothing to do." % output
+        print("%s is up to date. Nothing to do." % output)
         sys.exit(0)
 
     params_list = scan_defconfigs(jobs)

From 5e7c8a39e634235e2ee696a39bf1f404fc707fda Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Fri, 20 Sep 2019 17:42:08 -0400
Subject: [PATCH 2/7] genboardscfg.py: Remove "warnings" print section

We tell kconfiglib to not print any warnings to us so drop this code as
it will be unused.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
---
 tools/genboardscfg.py | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index e9a9c11865..9fd2bd30ef 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -165,11 +165,7 @@ class KconfigScanner:
                 else:
                     f.write(line[colon + 1:])
 
-        warnings = self._conf.load_config(self._tmpfile)
-        if warnings:
-            for warning in warnings:
-                print('%s: %s' % (defconfig, warning))
-
+        self._conf.load_config(self._tmpfile)
         try_remove(self._tmpfile)
         self._tmpfile = None
 

From 65e05ddc1ae25210a9865622e9e618e5ba8488c8 Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Fri, 20 Sep 2019 17:42:09 -0400
Subject: [PATCH 3/7] kconfiglib: Update to the 12.14.0 release

A large number of changes have happened upstream since our last sync
which was to 375506d.  The reason to do the upgrade at this point is for
improved Python 3 support.

As part of this upgrade we need to update moveconfig.py and
genboardscfg.py the current API.  This is:
- Change "kconfiglib.Config" calls to "kconfiglib.Kconfig"
- Change get_symbol() calls to syms.get().
- Change get_value() to str_value.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
---
 tools/buildman/kconfiglib.py | 9498 +++++++++++++++++++++++-----------
 tools/genboardscfg.py        |    6 +-
 tools/moveconfig.py          |   12 +-
 3 files changed, 6501 insertions(+), 3015 deletions(-)

diff --git a/tools/buildman/kconfiglib.py b/tools/buildman/kconfiglib.py
index d68af056b6..3908985c7b 100644
--- a/tools/buildman/kconfiglib.py
+++ b/tools/buildman/kconfiglib.py
@@ -1,3409 +1,6219 @@
+# Copyright (c) 2011-2019, Ulf Magnusson
 # SPDX-License-Identifier: ISC
-#
-# Author: Ulf Magnusson
-#   https://github.com/ulfalizer/Kconfiglib
-
-# This is Kconfiglib, a Python library for scripting, debugging, and extracting
-# information from Kconfig-based configuration systems. To view the
-# documentation, run
-#
-#  $ pydoc kconfiglib
-#
-# or, if you prefer HTML,
-#
-#  $ pydoc -w kconfiglib
-#
-# The examples/ subdirectory contains examples, to be run with e.g.
-#
-#  $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
-#
-# Look in testsuite.py for the test suite.
 
 """
-Kconfiglib is a Python library for scripting and extracting information from
-Kconfig-based configuration systems. Features include the following:
+Overview
+========
 
- - Symbol values and properties can be looked up and values assigned
-   programmatically.
- - .config files can be read and written.
- - Expressions can be evaluated in the context of a Kconfig configuration.
- - Relations between symbols can be quickly determined, such as finding all
-   symbols that reference a particular symbol.
- - Highly compatible with the scripts/kconfig/*conf utilities. The test suite
-   automatically compares outputs between Kconfiglib and the C implementation
-   for a large number of cases.
+Kconfiglib is a Python 2/3 library for scripting and extracting information
+from Kconfig (https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt)
+configuration systems.
 
-For the Linux kernel, scripts are run using
+See the homepage at https://github.com/ulfalizer/Kconfiglib for a longer
+overview.
 
- $ make scriptconfig [ARCH=<arch>] SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
+Since Kconfiglib 12.0.0, the library version is available in
+kconfiglib.VERSION, which is a (<major>, <minor>, <patch>) tuple, e.g.
+(12, 0, 0).
 
-Using the 'scriptconfig' target ensures that required environment variables
-(SRCARCH, ARCH, srctree, KERNELVERSION, etc.) are set up correctly.
 
-Scripts receive the name of the Kconfig file to load in sys.argv[1]. As of
-Linux 4.1.0-rc5, this is always "Kconfig" from the kernel top-level directory.
-If an argument is provided with SCRIPT_ARG, it appears as sys.argv[2].
+Using Kconfiglib on the Linux kernel with the Makefile targets
+==============================================================
 
-To get an interactive Python prompt with Kconfiglib preloaded and a Config
-object 'c' created, run
+For the Linux kernel, a handy interface is provided by the
+scripts/kconfig/Makefile patch, which can be applied with either 'git am' or
+the 'patch' utility:
 
- $ make iscriptconfig [ARCH=<arch>]
+  $ wget -qO- https://raw.githubusercontent.com/ulfalizer/Kconfiglib/master/makefile.patch | git am
+  $ wget -qO- https://raw.githubusercontent.com/ulfalizer/Kconfiglib/master/makefile.patch | patch -p1
 
-Kconfiglib supports both Python 2 and Python 3. For (i)scriptconfig, the Python
-interpreter to use can be passed in PYTHONCMD, which defaults to 'python'. PyPy
-works well too, and might give a nice speedup for long-running jobs.
+Warning: Not passing -p1 to patch will cause the wrong file to be patched.
 
-The examples/ directory contains short example scripts, which can be run with
-e.g.
+Please tell me if the patch does not apply. It should be trivial to apply
+manually, as it's just a block of text that needs to be inserted near the other
+*conf: targets in scripts/kconfig/Makefile.
 
- $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
+Look further down for a motivation for the Makefile patch and for instructions
+on how you can use Kconfiglib without it.
 
-or
+If you do not wish to install Kconfiglib via pip, the Makefile patch is set up
+so that you can also just clone Kconfiglib into the kernel root:
 
- $ make scriptconfig SCRIPT=Kconfiglib/examples/help_grep.py SCRIPT_ARG=kernel
+  $ git clone git://github.com/ulfalizer/Kconfiglib.git
+  $ git am Kconfiglib/makefile.patch  (or 'patch -p1 < Kconfiglib/makefile.patch')
 
-testsuite.py contains the test suite. See the top of the script for how to run
-it.
+Warning: The directory name Kconfiglib/ is significant in this case, because
+it's added to PYTHONPATH by the new targets in makefile.patch.
 
-Credits: Written by Ulf "Ulfalizer" Magnusson
+The targets added by the Makefile patch are described in the following
+sections.
 
-Send bug reports, suggestions and other feedback to ulfalizer a.t Google's
-email service. Don't wrestle with internal APIs. Tell me what you need and I
-might add it in a safe way as a client API instead."""
 
+make kmenuconfig
+----------------
+
+This target runs the curses menuconfig interface with Python 3. As of
+Kconfiglib 12.2.0, both Python 2 and Python 3 are supported (previously, only
+Python 3 was supported, so this was a backport).
+
+
+make guiconfig
+--------------
+
+This target runs the Tkinter menuconfig interface. Both Python 2 and Python 3
+are supported. To change the Python interpreter used, pass
+PYTHONCMD=<executable> to 'make'. The default is 'python'.
+
+
+make [ARCH=<arch>] iscriptconfig
+--------------------------------
+
+This target gives an interactive Python prompt where a Kconfig instance has
+been preloaded and is available in 'kconf'. To change the Python interpreter
+used, pass PYTHONCMD=<executable> to 'make'. The default is 'python'.
+
+To get a feel for the API, try evaluating and printing the symbols in
+kconf.defined_syms, and explore the MenuNode menu tree starting at
+kconf.top_node by following 'next' and 'list' pointers.
+
+The item contained in a menu node is found in MenuNode.item (note that this can
+be one of the constants kconfiglib.MENU and kconfiglib.COMMENT), and all
+symbols and choices have a 'nodes' attribute containing their menu nodes
+(usually only one). Printing a menu node will print its item, in Kconfig
+format.
+
+If you want to look up a symbol by name, use the kconf.syms dictionary.
+
+
+make scriptconfig SCRIPT=<script> [SCRIPT_ARG=<arg>]
+----------------------------------------------------
+
+This target runs the Python script given by the SCRIPT parameter on the
+configuration. sys.argv[1] holds the name of the top-level Kconfig file
+(currently always "Kconfig" in practice), and sys.argv[2] holds the SCRIPT_ARG
+argument, if given.
+
+See the examples/ subdirectory for example scripts.
+
+
+make dumpvarsconfig
+-------------------
+
+This target prints a list of all environment variables referenced from the
+Kconfig files, together with their values. See the
+Kconfiglib/examples/dumpvars.py script.
+
+Only environment variables that are referenced via the Kconfig preprocessor
+$(FOO) syntax are included. The preprocessor was added in Linux 4.18.
+
+
+Using Kconfiglib without the Makefile targets
+=============================================
+
+The make targets are only needed to pick up environment variables exported from
+the Kbuild makefiles and referenced inside Kconfig files, via e.g.
+'source "arch/$(SRCARCH)/Kconfig" and commands run via '$(shell,...)'.
+
+These variables are referenced as of writing (Linux 4.18), together with sample
+values:
+
+  srctree          (.)
+  ARCH             (x86)
+  SRCARCH          (x86)
+  KERNELVERSION    (4.18.0)
+  CC               (gcc)
+  HOSTCC           (gcc)
+  HOSTCXX          (g++)
+  CC_VERSION_TEXT  (gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0)
+
+Older kernels only reference ARCH, SRCARCH, and KERNELVERSION.
+
+If your kernel is recent enough (4.18+), you can get a list of referenced
+environment variables via 'make dumpvarsconfig' (see above). Note that this
+command is added by the Makefile patch.
+
+To run Kconfiglib without the Makefile patch, set the environment variables
+manually:
+
+  $ srctree=. ARCH=x86 SRCARCH=x86 KERNELVERSION=`make kernelversion` ... python(3)
+  >>> import kconfiglib
+  >>> kconf = kconfiglib.Kconfig()  # filename defaults to "Kconfig"
+
+Search the top-level Makefile for "Additional ARCH settings" to see other
+possibilities for ARCH and SRCARCH.
+
+
+Intro to symbol values
+======================
+
+Kconfiglib has the same assignment semantics as the C implementation.
+
+Any symbol can be assigned a value by the user (via Kconfig.load_config() or
+Symbol.set_value()), but this user value is only respected if the symbol is
+visible, which corresponds to it (currently) being visible in the menuconfig
+interface.
+
+For symbols with prompts, the visibility of the symbol is determined by the
+condition on the prompt. Symbols without prompts are never visible, so setting
+a user value on them is pointless. A warning will be printed by default if
+Symbol.set_value() is called on a promptless symbol. Assignments to promptless
+symbols are normal within a .config file, so no similar warning will be printed
+by load_config().
+
+Dependencies from parents and 'if'/'depends on' are propagated to properties,
+including prompts, so these two configurations are logically equivalent:
+
+(1)
+
+  menu "menu"
+      depends on A
+
+  if B
+
+  config FOO
+      tristate "foo" if D
+      default y
+      depends on C
+
+  endif
+
+  endmenu
+
+(2)
+
+  menu "menu"
+      depends on A
+
+  config FOO
+      tristate "foo" if A && B && C && D
+      default y if A && B && C
+
+  endmenu
+
+In this example, A && B && C && D (the prompt condition) needs to be non-n for
+FOO to be visible (assignable). If its value is m, the symbol can only be
+assigned the value m: The visibility sets an upper bound on the value that can
+be assigned by the user, and any higher user value will be truncated down.
+
+'default' properties are independent of the visibility, though a 'default' will
+often get the same condition as the prompt due to dependency propagation.
+'default' properties are used if the symbol is not visible or has no user
+value.
+
+Symbols with no user value (or that have a user value but are not visible) and
+no (active) 'default' default to n for bool/tristate symbols, and to the empty
+string for other symbol types.
+
+'select' works similarly to symbol visibility, but sets a lower bound on the
+value of the symbol. The lower bound is determined by the value of the
+select*ing* symbol. 'select' does not respect visibility, so non-visible
+symbols can be forced to a particular (minimum) value by a select as well.
+
+For non-bool/tristate symbols, it only matters whether the visibility is n or
+non-n: m visibility acts the same as y visibility.
+
+Conditions on 'default' and 'select' work in mostly intuitive ways. If the
+condition is n, the 'default' or 'select' is disabled. If it is m, the
+'default' or 'select' value (the value of the selecting symbol) is truncated
+down to m.
+
+When writing a configuration with Kconfig.write_config(), only symbols that are
+visible, have an (active) default, or are selected will get written out (note
+that this includes all symbols that would accept user values). Kconfiglib
+matches the .config format produced by the C implementations down to the
+character. This eases testing.
+
+For a visible bool/tristate symbol FOO with value n, this line is written to
+.config:
+
+    # CONFIG_FOO is not set
+
+The point is to remember the user n selection (which might differ from the
+default value the symbol would get), while at the same sticking to the rule
+that undefined corresponds to n (.config uses Makefile format, making the line
+above a comment). When the .config file is read back in, this line will be
+treated the same as the following assignment:
+
+    CONFIG_FOO=n
+
+In Kconfiglib, the set of (currently) assignable values for a bool/tristate
+symbol appear in Symbol.assignable. For other symbol types, just check if
+sym.visibility is non-0 (non-n) to see whether the user value will have an
+effect.
+
+
+Intro to the menu tree
+======================
+
+The menu structure, as seen in e.g. menuconfig, is represented by a tree of
+MenuNode objects. The top node of the configuration corresponds to an implicit
+top-level menu, the title of which is shown at the top in the standard
+menuconfig interface. (The title is also available in Kconfig.mainmenu_text in
+Kconfiglib.)
+
+The top node is found in Kconfig.top_node. From there, you can visit child menu
+nodes by following the 'list' pointer, and any following menu nodes by
+following the 'next' pointer. Usually, a non-None 'list' pointer indicates a
+menu or Choice, but menu nodes for symbols can sometimes have a non-None 'list'
+pointer too due to submenus created implicitly from dependencies.
+
+MenuNode.item is either a Symbol or a Choice object, or one of the constants
+MENU and COMMENT. The prompt of the menu node can be found in MenuNode.prompt,
+which also holds the title for menus and comments. For Symbol and Choice,
+MenuNode.help holds the help text (if any, otherwise None).
+
+Most symbols will only have a single menu node. A symbol defined in multiple
+locations will have one menu node for each location. The list of menu nodes for
+a Symbol or Choice can be found in the Symbol/Choice.nodes attribute.
+
+Note that prompts and help texts for symbols and choices are stored in their
+menu node(s) rather than in the Symbol or Choice objects themselves. This makes
+it possible to define a symbol in multiple locations with a different prompt or
+help text in each location. To get the help text or prompt for a symbol with a
+single menu node, do sym.nodes[0].help and sym.nodes[0].prompt, respectively.
+The prompt is a (text, condition) tuple, where condition determines the
+visibility (see 'Intro to expressions' below).
+
+This organization mirrors the C implementation. MenuNode is called
+'struct menu' there, but I thought "menu" was a confusing name.
+
+It is possible to give a Choice a name and define it in multiple locations,
+hence why Choice.nodes is also a list.
+
+As a convenience, the properties added at a particular definition location are
+available on the MenuNode itself, in e.g. MenuNode.defaults. This is helpful
+when generating documentation, so that symbols/choices defined in multiple
+locations can be shown with the correct properties at each location.
+
+
+Intro to expressions
+====================
+
+Expressions can be evaluated with the expr_value() function and printed with
+the expr_str() function (these are used internally as well). Evaluating an
+expression always yields a tristate value, where n, m, and y are represented as
+0, 1, and 2, respectively.
+
+The following table should help you figure out how expressions are represented.
+A, B, C, ... are symbols (Symbol instances), NOT is the kconfiglib.NOT
+constant, etc.
+
+Expression            Representation
+----------            --------------
+A                     A
+"A"                   A (constant symbol)
+!A                    (NOT, A)
+A && B                (AND, A, B)
+A && B && C           (AND, A, (AND, B, C))
+A || B                (OR, A, B)
+A || (B && C && D)    (OR, A, (AND, B, (AND, C, D)))
+A = B                 (EQUAL, A, B)
+A != "foo"            (UNEQUAL, A, foo (constant symbol))
+A && B = C && D       (AND, A, (AND, (EQUAL, B, C), D))
+n                     Kconfig.n (constant symbol)
+m                     Kconfig.m (constant symbol)
+y                     Kconfig.y (constant symbol)
+"y"                   Kconfig.y (constant symbol)
+
+Strings like "foo" in 'default "foo"' or 'depends on SYM = "foo"' are
+represented as constant symbols, so the only values that appear in expressions
+are symbols***. This mirrors the C implementation.
+
+***For choice symbols, the parent Choice will appear in expressions as well,
+but it's usually invisible as the value interfaces of Symbol and Choice are
+identical. This mirrors the C implementation and makes different choice modes
+"just work".
+
+Manual evaluation examples:
+
+  - The value of A && B is min(A.tri_value, B.tri_value)
+
+  - The value of A || B is max(A.tri_value, B.tri_value)
+
+  - The value of !A is 2 - A.tri_value
+
+  - The value of A = B is 2 (y) if A.str_value == B.str_value, and 0 (n)
+    otherwise. Note that str_value is used here instead of tri_value.
+
+    For constant (as well as undefined) symbols, str_value matches the name of
+    the symbol. This mirrors the C implementation and explains why
+    'depends on SYM = "foo"' above works as expected.
+
+n/m/y are automatically converted to the corresponding constant symbols
+"n"/"m"/"y" (Kconfig.n/m/y) during parsing.
+
+Kconfig.const_syms is a dictionary like Kconfig.syms but for constant symbols.
+
+If a condition is missing (e.g., <cond> when the 'if <cond>' is removed from
+'default A if <cond>'), it is actually Kconfig.y. The standard __str__()
+functions just avoid printing 'if y' conditions to give cleaner output.
+
+
+Kconfig extensions
+==================
+
+Kconfiglib includes a couple of Kconfig extensions:
+
+'source' with relative path
+---------------------------
+
+The 'rsource' statement sources Kconfig files with a path relative to directory
+of the Kconfig file containing the 'rsource' statement, instead of relative to
+the project root.
+
+Consider following directory tree:
+
+  Project
+  +--Kconfig
+  |
+  +--src
+     +--Kconfig
+     |
+     +--SubSystem1
+        +--Kconfig
+        |
+        +--ModuleA
+           +--Kconfig
+
+In this example, assume that src/SubSystem1/Kconfig wants to source
+src/SubSystem1/ModuleA/Kconfig.
+
+With 'source', this statement would be used:
+
+  source "src/SubSystem1/ModuleA/Kconfig"
+
+With 'rsource', this turns into
+
+  rsource "ModuleA/Kconfig"
+
+If an absolute path is given to 'rsource', it acts the same as 'source'.
+
+'rsource' can be used to create "position-independent" Kconfig trees that can
+be moved around freely.
+
+
+Globbing 'source'
+-----------------
+
+'source' and 'rsource' accept glob patterns, sourcing all matching Kconfig
+files. They require at least one matching file, raising a KconfigError
+otherwise.
+
+For example, the following statement might source sub1/foofoofoo and
+sub2/foobarfoo:
+
+  source "sub[12]/foo*foo"
+
+The glob patterns accepted are the same as for the standard glob.glob()
+function.
+
+Two additional statements are provided for cases where it's acceptable for a
+pattern to match no files: 'osource' and 'orsource' (the o is for "optional").
+
+For example, the following statements will be no-ops if neither "foo" nor any
+files matching "bar*" exist:
+
+  osource "foo"
+  osource "bar*"
+
+'orsource' does a relative optional source.
+
+'source' and 'osource' are analogous to 'include' and '-include' in Make.
+
+
+Generalized def_* keywords
+--------------------------
+
+def_int, def_hex, and def_string are available in addition to def_bool and
+def_tristate, allowing int, hex, and string symbols to be given a type and a
+default at the same time.
+
+
+Extra optional warnings
+-----------------------
+
+Some optional warnings can be controlled via environment variables:
+
+  - KCONFIG_WARN_UNDEF: If set to 'y', warnings will be generated for all
+    references to undefined symbols within Kconfig files. The only gotcha is
+    that all hex literals must be prefixed with "0x" or "0X", to make it
+    possible to distinguish them from symbol references.
+
+    Some projects (e.g. the Linux kernel) use multiple Kconfig trees with many
+    shared Kconfig files, leading to some safe undefined symbol references.
+    KCONFIG_WARN_UNDEF is useful in projects that only have a single Kconfig
+    tree though.
+
+    KCONFIG_STRICT is an older alias for this environment variable, supported
+    for backwards compatibility.
+
+  - KCONFIG_WARN_UNDEF_ASSIGN: If set to 'y', warnings will be generated for
+    all assignments to undefined symbols within .config files. By default, no
+    such warnings are generated.
+
+    This warning can also be enabled/disabled via the Kconfig.warn_assign_undef
+    variable.
+
+
+Preprocessor user functions defined in Python
+---------------------------------------------
+
+Preprocessor functions can be defined in Python, which makes it simple to
+integrate information from existing Python tools into Kconfig (e.g. to have
+Kconfig symbols depend on hardware information stored in some other format).
+
+Putting a Python module named kconfigfunctions(.py) anywhere in sys.path will
+cause it to be imported by Kconfiglib (in Kconfig.__init__()). Note that
+sys.path can be customized via PYTHONPATH, and includes the directory of the
+module being run by default, as well as installation directories.
+
+If the KCONFIG_FUNCTIONS environment variable is set, it gives a different
+module name to use instead of 'kconfigfunctions'.
+
+The imported module is expected to define a global dictionary named 'functions'
+that maps function names to Python functions, as follows:
+
+  def my_fn(kconf, name, arg_1, arg_2, ...):
+      # kconf:
+      #   Kconfig instance
+      #
+      # name:
+      #   Name of the user-defined function ("my-fn"). Think argv[0].
+      #
+      # arg_1, arg_2, ...:
+      #   Arguments passed to the function from Kconfig (strings)
+      #
+      # Returns a string to be substituted as the result of calling the
+      # function
+      ...
+
+  def my_other_fn(kconf, name, arg_1, arg_2, ...):
+      ...
+
+  functions = {
+      "my-fn":       (my_fn,       <min.args>, <max.args>/None),
+      "my-other-fn": (my_other_fn, <min.args>, <max.args>/None),
+      ...
+  }
+
+  ...
+
+<min.args> and <max.args> are the minimum and maximum number of arguments
+expected by the function (excluding the implicit 'name' argument). If
+<max.args> is None, there is no upper limit to the number of arguments. Passing
+an invalid number of arguments will generate a KconfigError exception.
+
+Functions can access the current parsing location as kconf.filename/linenr.
+Accessing other fields of the Kconfig object is not safe. See the warning
+below.
+
+Keep in mind that for a variable defined like 'foo = $(fn)', 'fn' will be
+called only when 'foo' is expanded. If 'fn' uses the parsing location and the
+intent is to use the location of the assignment, you want 'foo := $(fn)'
+instead, which calls the function immediately.
+
+Once defined, user functions can be called from Kconfig in the same way as
+other preprocessor functions:
+
+    config FOO
+        ...
+        depends on $(my-fn,arg1,arg2)
+
+If my_fn() returns "n", this will result in
+
+    config FOO
+        ...
+        depends on n
+
+Warning
+*******
+
+User-defined preprocessor functions are called as they're encountered at parse
+time, before all Kconfig files have been processed, and before the menu tree
+has been finalized. There are no guarantees that accessing Kconfig symbols or
+the menu tree via the 'kconf' parameter will work, and it could potentially
+lead to a crash.
+
+Preferably, user-defined functions should be stateless.
+
+
+Feedback
+========
+
+Send bug reports, suggestions, and questions to ulfalizer a.t Google's email
+service, or open a ticket on the GitHub page.
+"""
+import errno
+import importlib
 import os
-import platform
 import re
 import sys
 
+# Get rid of some attribute lookups. These are obvious in context.
+from glob import iglob
+from os.path import dirname, exists, expandvars, islink, join, realpath
+
+
+VERSION = (12, 14, 0)
+
+
 # File layout:
 #
 # Public classes
 # Public functions
-# Internal classes
 # Internal functions
-# Internal global constants
+# Global constants
 
 # Line length: 79 columns
 
+
 #
 # Public classes
 #
 
-class Config(object):
 
-    """Represents a Kconfig configuration, e.g. for i386 or ARM. This is the
-    set of symbols and other items appearing in the configuration together with
-    their values. Creating any number of Config objects -- including for
-    different architectures -- is safe; Kconfiglib has no global state."""
+class Kconfig(object):
+    """
+    Represents a Kconfig configuration, e.g. for x86 or ARM. This is the set of
+    symbols, choices, and menu nodes appearing in the configuration. Creating
+    any number of Kconfig objects (including for different architectures) is
+    safe. Kconfiglib doesn't keep any global state.
+
+    The following attributes are available. They should be treated as
+    read-only, and some are implemented through @property magic.
+
+    syms:
+      A dictionary with all symbols in the configuration, indexed by name. Also
+      includes all symbols that are referenced in expressions but never
+      defined, except for constant (quoted) symbols.
+
+      Undefined symbols can be recognized by Symbol.nodes being empty -- see
+      the 'Intro to the menu tree' section in the module docstring.
+
+    const_syms:
+      A dictionary like 'syms' for constant (quoted) symbols
+
+    named_choices:
+      A dictionary like 'syms' for named choices (choice FOO)
+
+    defined_syms:
+      A list with all defined symbols, in the same order as they appear in the
+      Kconfig files. Symbols defined in multiple locations appear multiple
+      times.
+
+      Note: You probably want to use 'unique_defined_syms' instead. This
+      attribute is mostly maintained for backwards compatibility.
+
+    unique_defined_syms:
+      A list like 'defined_syms', but with duplicates removed. Just the first
+      instance is kept for symbols defined in multiple locations. Kconfig order
+      is preserved otherwise.
+
+      Using this attribute instead of 'defined_syms' can save work, and
+      automatically gives reasonable behavior when writing configuration output
+      (symbols defined in multiple locations only generate output once, while
+      still preserving Kconfig order for readability).
+
+    choices:
+      A list with all choices, in the same order as they appear in the Kconfig
+      files.
+
+      Note: You probably want to use 'unique_choices' instead. This attribute
+      is mostly maintained for backwards compatibility.
+
+    unique_choices:
+      Analogous to 'unique_defined_syms', for choices. Named choices can have
+      multiple definition locations.
+
+    menus:
+      A list with all menus, in the same order as they appear in the Kconfig
+      files
+
+    comments:
+      A list with all comments, in the same order as they appear in the Kconfig
+      files
+
+    kconfig_filenames:
+      A list with the filenames of all Kconfig files included in the
+      configuration, relative to $srctree (or relative to the current directory
+      if $srctree isn't set), except absolute paths (e.g.
+      'source "/foo/Kconfig"') are kept as-is.
+
+      The files are listed in the order they are source'd, starting with the
+      top-level Kconfig file. If a file is source'd multiple times, it will
+      appear multiple times. Use set() to get unique filenames.
+
+      Note that Kconfig.sync_deps() already indirectly catches any file
+      modifications that change configuration output.
+
+    env_vars:
+      A set() with the names of all environment variables referenced in the
+      Kconfig files.
+
+      Only environment variables referenced with the preprocessor $(FOO) syntax
+      will be registered. The older $FOO syntax is only supported for backwards
+      compatibility.
+
+      Also note that $(FOO) won't be registered unless the environment variable
+      $FOO is actually set. If it isn't, $(FOO) is an expansion of an unset
+      preprocessor variable (which gives the empty string).
+
+      Another gotcha is that environment variables referenced in the values of
+      recursively expanded preprocessor variables (those defined with =) will
+      only be registered if the variable is actually used (expanded) somewhere.
+
+      The note from the 'kconfig_filenames' documentation applies here too.
+
+    n/m/y:
+      The predefined constant symbols n/m/y. Also available in const_syms.
+
+    modules:
+      The Symbol instance for the modules symbol. Currently hardcoded to
+      MODULES, which is backwards compatible. Kconfiglib will warn if
+      'option modules' is set on some other symbol. Tell me if you need proper
+      'option modules' support.
+
+      'modules' is never None. If the MODULES symbol is not explicitly defined,
+      its tri_value will be 0 (n), as expected.
+
+      A simple way to enable modules is to do 'kconf.modules.set_value(2)'
+      (provided the MODULES symbol is defined and visible). Modules are
+      disabled by default in the kernel Kconfig files as of writing, though
+      nearly all defconfig files enable them (with 'CONFIG_MODULES=y').
+
+    defconfig_list:
+      The Symbol instance for the 'option defconfig_list' symbol, or None if no
+      defconfig_list symbol exists. The defconfig filename derived from this
+      symbol can be found in Kconfig.defconfig_filename.
+
+    defconfig_filename:
+      The filename given by the defconfig_list symbol. This is taken from the
+      first 'default' with a satisfied condition where the specified file
+      exists (can be opened for reading). If a defconfig file foo/defconfig is
+      not found and $srctree was set when the Kconfig was created,
+      $srctree/foo/defconfig is looked up as well.
+
+      'defconfig_filename' is None if either no defconfig_list symbol exists,
+      or if the defconfig_list symbol has no 'default' with a satisfied
+      condition that specifies a file that exists.
+
+      Gotcha: scripts/kconfig/Makefile might pass --defconfig=<defconfig> to
+      scripts/kconfig/conf when running e.g. 'make defconfig'. This option
+      overrides the defconfig_list symbol, meaning defconfig_filename might not
+      always match what 'make defconfig' would use.
+
+    top_node:
+      The menu node (see the MenuNode class) of the implicit top-level menu.
+      Acts as the root of the menu tree.
+
+    mainmenu_text:
+      The prompt (title) of the top menu (top_node). Defaults to "Main menu".
+      Can be changed with the 'mainmenu' statement (see kconfig-language.txt).
+
+    variables:
+      A dictionary with all preprocessor variables, indexed by name. See the
+      Variable class.
+
+    warn:
+      Set this variable to True/False to enable/disable warnings. See
+      Kconfig.__init__().
+
+      When 'warn' is False, the values of the other warning-related variables
+      are ignored.
+
+      This variable as well as the other warn* variables can be read to check
+      the current warning settings.
+
+    warn_to_stderr:
+      Set this variable to True/False to enable/disable warnings on stderr. See
+      Kconfig.__init__().
+
+    warn_assign_undef:
+      Set this variable to True to generate warnings for assignments to
+      undefined symbols in configuration files.
+
+      This variable is False by default unless the KCONFIG_WARN_UNDEF_ASSIGN
+      environment variable was set to 'y' when the Kconfig instance was
+      created.
+
+    warn_assign_override:
+      Set this variable to True to generate warnings for multiple assignments
+      to the same symbol in configuration files, where the assignments set
+      different values (e.g. CONFIG_FOO=m followed by CONFIG_FOO=y, where the
+      last value would get used).
+
+      This variable is True by default. Disabling it might be useful when
+      merging configurations.
+
+    warn_assign_redun:
+      Like warn_assign_override, but for multiple assignments setting a symbol
+      to the same value.
+
+      This variable is True by default. Disabling it might be useful when
+      merging configurations.
+
+    warnings:
+      A list of strings containing all warnings that have been generated, for
+      cases where more flexibility is needed.
+
+      See the 'warn_to_stderr' parameter to Kconfig.__init__() and the
+      Kconfig.warn_to_stderr variable as well. Note that warnings still get
+      added to Kconfig.warnings when 'warn_to_stderr' is True.
+
+      Just as for warnings printed to stderr, only warnings that are enabled
+      will get added to Kconfig.warnings. See the various Kconfig.warn*
+      variables.
+
+    missing_syms:
+      A list with (name, value) tuples for all assignments to undefined symbols
+      within the most recently loaded .config file(s). 'name' is the symbol
+      name without the 'CONFIG_' prefix. 'value' is a string that gives the
+      right-hand side of the assignment verbatim.
+
+      See Kconfig.load_config() as well.
+
+    srctree:
+      The value of the $srctree environment variable when the configuration was
+      loaded, or the empty string if $srctree wasn't set. This gives nice
+      behavior with os.path.join(), which treats "" as the current directory,
+      without adding "./".
+
+      Kconfig files are looked up relative to $srctree (unless absolute paths
+      are used), and .config files are looked up relative to $srctree if they
+      are not found in the current directory. This is used to support
+      out-of-tree builds. The C tools use this environment variable in the same
+      way.
+
+      Changing $srctree after creating the Kconfig instance has no effect. Only
+      the value when the configuration is loaded matters. This avoids surprises
+      if multiple configurations are loaded with different values for $srctree.
+
+    config_prefix:
+      The value of the $CONFIG_ environment variable when the configuration was
+      loaded. This is the prefix used (and expected) on symbol names in .config
+      files and C headers. Defaults to "CONFIG_". Used in the same way in the C
+      tools.
+
+      Like for srctree, only the value of $CONFIG_ when the configuration is
+      loaded matters.
+
+    filename/linenr:
+      The current parsing location, for use in Python preprocessor functions.
+      See the module docstring.
+    """
+    __slots__ = (
+        "_encoding",
+        "_functions",
+        "_set_match",
+        "_srctree_prefix",
+        "_unset_match",
+        "_warn_assign_no_prompt",
+        "choices",
+        "comments",
+        "config_prefix",
+        "const_syms",
+        "defconfig_list",
+        "defined_syms",
+        "env_vars",
+        "kconfig_filenames",
+        "m",
+        "menus",
+        "missing_syms",
+        "modules",
+        "n",
+        "named_choices",
+        "srctree",
+        "syms",
+        "top_node",
+        "unique_choices",
+        "unique_defined_syms",
+        "variables",
+        "warn",
+        "warn_assign_override",
+        "warn_assign_redun",
+        "warn_assign_undef",
+        "warn_to_stderr",
+        "warnings",
+        "y",
+
+        # Parsing-related
+        "_parsing_kconfigs",
+        "_readline",
+        "filename",
+        "linenr",
+        "_include_path",
+        "_filestack",
+        "_line",
+        "_tokens",
+        "_tokens_i",
+        "_reuse_tokens",
+    )
 
     #
     # Public interface
     #
 
-    def __init__(self, filename="Kconfig", base_dir=None, print_warnings=True,
-                 print_undef_assign=False):
-        """Creates a new Config object, representing a Kconfig configuration.
-        Raises Kconfig_Syntax_Error on syntax errors.
+    def __init__(self, filename="Kconfig", warn=True, warn_to_stderr=True,
+                 encoding="utf-8"):
+        """
+        Creates a new Kconfig object by parsing Kconfig files.
+        Note that Kconfig files are not the same as .config files (which store
+        configuration symbol values).
 
-        filename (default: "Kconfig"): The base Kconfig file of the
-           configuration. For the Linux kernel, you'll probably want "Kconfig"
-           from the top-level directory, as environment variables will make
-           sure the right Kconfig is included from there
-           (arch/<architecture>/Kconfig). If you are using Kconfiglib via 'make
-           scriptconfig', the filename of the base base Kconfig file will be in
-           sys.argv[1].
+        See the module docstring for some environment variables that influence
+        default warning settings (KCONFIG_WARN_UNDEF and
+        KCONFIG_WARN_UNDEF_ASSIGN).
 
-        base_dir (default: None): The base directory relative to which 'source'
-           statements within Kconfig files will work. For the Linux kernel this
-           should be the top-level directory of the kernel tree. $-references
-           to existing environment variables will be expanded.
+        Raises KconfigError on syntax/semantic errors, and OSError or (possibly
+        a subclass of) IOError on IO errors ('errno', 'strerror', and
+        'filename' are available). Note that IOError is an alias for OSError on
+        Python 3, so it's enough to catch OSError there. If you need Python 2/3
+        compatibility, it's easiest to catch EnvironmentError, which is a
+        common base class of OSError/IOError on Python 2 and an alias for
+        OSError on Python 3.
 
-           If None (the default), the environment variable 'srctree' will be
-           used if set, and the current directory otherwise. 'srctree' is set
-           by the Linux makefiles to the top-level kernel directory. A default
-           of "." would not work with an alternative build directory.
+        filename (default: "Kconfig"):
+          The Kconfig file to load. For the Linux kernel, you'll want "Kconfig"
+          from the top-level directory, as environment variables will make sure
+          the right Kconfig is included from there (arch/$SRCARCH/Kconfig as of
+          writing).
 
-        print_warnings (default: True): Set to True if warnings related to this
-           configuration should be printed to stderr. This can be changed later
-           with Config.set_print_warnings(). It is provided as a constructor
-           argument since warnings might be generated during parsing.
+          If $srctree is set, 'filename' will be looked up relative to it.
+          $srctree is also used to look up source'd files within Kconfig files.
+          See the class documentation.
 
-        print_undef_assign (default: False): Set to True if informational
-           messages related to assignments to undefined symbols should be
-           printed to stderr for this configuration. Can be changed later with
-           Config.set_print_undef_assign()."""
+          If you are using Kconfiglib via 'make scriptconfig', the filename of
+          the base base Kconfig file will be in sys.argv[1]. It's currently
+          always "Kconfig" in practice.
+
+        warn (default: True):
+          True if warnings related to this configuration should be generated.
+          This can be changed later by setting Kconfig.warn to True/False. It
+          is provided as a constructor argument since warnings might be
+          generated during parsing.
+
+          See the other Kconfig.warn_* variables as well, which enable or
+          suppress certain warnings when warnings are enabled.
+
+          All generated warnings are added to the Kconfig.warnings list. See
+          the class documentation.
+
+        warn_to_stderr (default: True):
+          True if warnings should be printed to stderr in addition to being
+          added to Kconfig.warnings.
+
+          This can be changed later by setting Kconfig.warn_to_stderr to
+          True/False.
+
+        encoding (default: "utf-8"):
+          The encoding to use when reading and writing files, and when decoding
+          output from commands run via $(shell). If None, the encoding
+          specified in the current locale will be used.
+
+          The "utf-8" default avoids exceptions on systems that are configured
+          to use the C locale, which implies an ASCII encoding.
+
+          This parameter has no effect on Python 2, due to implementation
+          issues (regular strings turning into Unicode strings, which are
+          distinct in Python 2). Python 2 doesn't decode regular strings
+          anyway.
+
+          Related PEP: https://www.python.org/dev/peps/pep-0538/
+        """
+        self._encoding = encoding
+
+        self.srctree = os.getenv("srctree", "")
+        # A prefix we can reliably strip from glob() results to get a filename
+        # relative to $srctree. relpath() can cause issues for symlinks,
+        # because it assumes symlink/../foo is the same as foo/.
+        self._srctree_prefix = realpath(self.srctree) + os.sep
+
+        self.warn = warn
+        self.warn_to_stderr = warn_to_stderr
+        self.warn_assign_undef = os.getenv("KCONFIG_WARN_UNDEF_ASSIGN") == "y"
+        self.warn_assign_override = True
+        self.warn_assign_redun = True
+        self._warn_assign_no_prompt = True
+
+        self.warnings = []
+
+        self.config_prefix = os.getenv("CONFIG_", "CONFIG_")
+        # Regular expressions for parsing .config files
+        self._set_match = _re_match(self.config_prefix + r"([^=]+)=(.*)")
+        self._unset_match = _re_match(r"# {}([^ ]+) is not set".format(
+            self.config_prefix))
 
-        # The set of all symbols, indexed by name (a string)
         self.syms = {}
-        # Python 2/3 compatibility hack. This is the only one needed.
-        self.syms_iter = self.syms.values if sys.version_info[0] >= 3 else \
-                         self.syms.itervalues
-
-        # The set of all defined symbols in the configuration in the order they
-        # appear in the Kconfig files. This excludes the special symbols n, m,
-        # and y as well as symbols that are referenced but never defined.
-        self.kconfig_syms = []
-
-        # The set of all named choices (yes, choices can have names), indexed
-        # by name (a string)
+        self.const_syms = {}
+        self.defined_syms = []
+        self.missing_syms = []
         self.named_choices = {}
-
-        # Lists containing all choices, menus and comments in the configuration
         self.choices = []
         self.menus = []
         self.comments = []
 
-        def register_special_symbol(type_, name, val):
+        for nmy in "n", "m", "y":
             sym = Symbol()
-            sym.is_special_ = True
-            sym.is_defined_ = True
-            sym.config = self
-            sym.name = name
-            sym.type = type_
-            sym.cached_val = val
-            self.syms[name] = sym
-            return sym
+            sym.kconfig = self
+            sym.name = nmy
+            sym.is_constant = True
+            sym.orig_type = TRISTATE
+            sym._cached_tri_val = STR_TO_TRI[nmy]
 
-        # The special symbols n, m and y, used as shorthand for "n", "m" and
-        # "y"
-        self.n = register_special_symbol(TRISTATE, "n", "n")
-        self.m = register_special_symbol(TRISTATE, "m", "m")
-        self.y = register_special_symbol(TRISTATE, "y", "y")
-        # DEFCONFIG_LIST uses this
-        register_special_symbol(STRING, "UNAME_RELEASE", platform.uname()[2])
+            self.const_syms[nmy] = sym
 
-        # The symbol with "option defconfig_list" set, containing a list of
-        # default .config files
-        self.defconfig_sym = None
+        self.n = self.const_syms["n"]
+        self.m = self.const_syms["m"]
+        self.y = self.const_syms["y"]
 
-        # See Symbol.get_(src)arch()
-        self.arch = os.environ.get("ARCH")
-        self.srcarch = os.environ.get("SRCARCH")
+        # Make n/m/y well-formed symbols
+        for nmy in "n", "m", "y":
+            sym = self.const_syms[nmy]
+            sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
 
-        # If you set CONFIG_ in the environment, Kconfig will prefix all symbols
-        # with its value when saving the configuration, instead of using the default, "CONFIG_".
-        self.config_prefix = os.environ.get("CONFIG_")
-        if self.config_prefix is None:
-            self.config_prefix = "CONFIG_"
+        # Maps preprocessor variables names to Variable instances
+        self.variables = {}
 
-        # See Config.__init__(). We need this for get_defconfig_filename().
-        self.srctree = os.environ.get("srctree")
-        if self.srctree is None:
-            self.srctree = "."
+        # Predefined preprocessor functions, with min/max number of arguments
+        self._functions = {
+            "info":       (_info_fn,       1, 1),
+            "error-if":   (_error_if_fn,   2, 2),
+            "filename":   (_filename_fn,   0, 0),
+            "lineno":     (_lineno_fn,     0, 0),
+            "shell":      (_shell_fn,      1, 1),
+            "warning-if": (_warning_if_fn, 2, 2),
+        }
 
-        self.filename = filename
-        self.base_dir = self.srctree if base_dir is None else \
-                        os.path.expandvars(base_dir)
+        # Add any user-defined preprocessor functions
+        try:
+            self._functions.update(
+                importlib.import_module(
+                    os.getenv("KCONFIG_FUNCTIONS", "kconfigfunctions")
+                ).functions)
+        except ImportError:
+            pass
 
-        # The 'mainmenu' text
-        self.mainmenu_text = None
+        # This determines whether previously unseen symbols are registered.
+        # They shouldn't be if we parse expressions after parsing, as part of
+        # Kconfig.eval_string().
+        self._parsing_kconfigs = True
 
-        # The filename of the most recently loaded .config file
-        self.config_filename = None
-        # The textual header of the most recently loaded .config, uncommented
-        self.config_header = None
+        self.modules = self._lookup_sym("MODULES")
+        self.defconfig_list = None
 
-        self.print_warnings = print_warnings
-        self.print_undef_assign = print_undef_assign
-        self._warnings = []
-
-        # For parsing routines that stop when finding a line belonging to a
-        # different construct, these holds that line and the tokenized version
-        # of that line. The purpose is to avoid having to re-tokenize the line,
-        # which is inefficient and causes problems when recording references to
-        # symbols.
-        self.end_line = None
-        self.end_line_tokens = None
-
-        # See the comment in _parse_expr().
-        self._cur_item = None
-        self._line = None
-        self._filename = None
-        self._linenr = None
-        self._transform_m = None
+        self.top_node = MenuNode()
+        self.top_node.kconfig = self
+        self.top_node.item = MENU
+        self.top_node.is_menuconfig = True
+        self.top_node.visibility = self.y
+        self.top_node.prompt = ("Main menu", self.y)
+        self.top_node.parent = None
+        self.top_node.dep = self.y
+        self.top_node.filename = filename
+        self.top_node.linenr = 1
+        self.top_node.include_path = ()
 
         # Parse the Kconfig files
-        self.top_block = []
-        self._parse_file(filename, None, None, None, self.top_block)
 
-        # Build Symbol.dep for all symbols
+        # Not used internally. Provided as a convenience.
+        self.kconfig_filenames = [filename]
+        self.env_vars = set()
+
+        # Keeps track of the location in the parent Kconfig files. Kconfig
+        # files usually source other Kconfig files. See _enter_file().
+        self._filestack = []
+        self._include_path = ()
+
+        # The current parsing location
+        self.filename = filename
+        self.linenr = 0
+
+        # Used to avoid retokenizing lines when we discover that they're not
+        # part of the construct currently being parsed. This is kinda like an
+        # unget operation.
+        self._reuse_tokens = False
+
+        # Open the top-level Kconfig file. Store the readline() method directly
+        # as a small optimization.
+        self._readline = self._open(join(self.srctree, filename), "r").readline
+
+        try:
+            # Parse the Kconfig files
+            self._parse_block(None, self.top_node, self.top_node)
+            self.top_node.list = self.top_node.next
+            self.top_node.next = None
+        except UnicodeDecodeError as e:
+            _decoding_error(e, self.filename)
+
+        # Close the top-level Kconfig file. __self__ fetches the 'file' object
+        # for the method.
+        self._readline.__self__.close()
+
+        self._parsing_kconfigs = False
+
+        # Do various menu tree post-processing
+        self._finalize_node(self.top_node, self.y)
+
+        self.unique_defined_syms = _ordered_unique(self.defined_syms)
+        self.unique_choices = _ordered_unique(self.choices)
+
+        # Do sanity checks. Some of these depend on everything being finalized.
+        self._check_sym_sanity()
+        self._check_choice_sanity()
+
+        # KCONFIG_STRICT is an older alias for KCONFIG_WARN_UNDEF, supported
+        # for backwards compatibility
+        if os.getenv("KCONFIG_WARN_UNDEF") == "y" or \
+           os.getenv("KCONFIG_STRICT") == "y":
+
+            self._check_undef_syms()
+
+        # Build Symbol._dependents for all symbols and choices
         self._build_dep()
 
-    def get_arch(self):
-        """Returns the value the environment variable ARCH had at the time the
-        Config instance was created, or None if ARCH was not set. For the
-        kernel, this corresponds to the architecture being built for, with
-        values such as "i386" or "mips"."""
-        return self.arch
+        # Check for dependency loops
+        check_dep_loop_sym = _check_dep_loop_sym  # Micro-optimization
+        for sym in self.unique_defined_syms:
+            check_dep_loop_sym(sym, False)
 
-    def get_srcarch(self):
-        """Returns the value the environment variable SRCARCH had at the time
-        the Config instance was created, or None if SRCARCH was not set. For
-        the kernel, this corresponds to the particular arch/ subdirectory
-        containing architecture-specific code."""
-        return self.srcarch
+        # Add extra dependencies from choices to choice symbols that get
+        # awkward during dependency loop detection
+        self._add_choice_deps()
 
-    def get_srctree(self):
-        """Returns the value the environment variable srctree had at the time
-        the Config instance was created, or None if srctree was not defined.
-        This variable points to the source directory and is used when building
-        in a separate directory."""
-        return self.srctree
-
-    def get_base_dir(self):
-        """Returns the base directory relative to which 'source' statements
-        will work, passed as an argument to Config.__init__()."""
-        return self.base_dir
-
-    def get_kconfig_filename(self):
-        """Returns the name of the (base) kconfig file this configuration was
-        loaded from."""
-        return self.filename
-
-    def get_config_filename(self):
-        """Returns the filename of the most recently loaded configuration file,
-        or None if no configuration has been loaded."""
-        return self.config_filename
-
-    def get_config_header(self):
-        """Returns the (uncommented) textual header of the .config file most
-        recently loaded with load_config(). Returns None if no .config file has
-        been loaded or if the most recently loaded .config file has no header.
-        The header consists of all lines up to but not including the first line
-        that either
-
-        1. Does not start with "#"
-        2. Has the form "# CONFIG_FOO is not set."
+    @property
+    def mainmenu_text(self):
         """
-        return self.config_header
+        See the class documentation.
+        """
+        return self.top_node.prompt[0]
 
-    def get_mainmenu_text(self):
-        """Returns the text of the 'mainmenu' statement (with $-references to
-        symbols replaced by symbol values), or None if the configuration has no
-        'mainmenu' statement."""
-        return None if self.mainmenu_text is None else \
-          self._expand_sym_refs(self.mainmenu_text)
+    @property
+    def defconfig_filename(self):
+        """
+        See the class documentation.
+        """
+        if self.defconfig_list:
+            for filename, cond in self.defconfig_list.defaults:
+                if expr_value(cond):
+                    try:
+                        with self._open_config(filename.str_value) as f:
+                            return f.name
+                    except EnvironmentError:
+                        continue
 
-    def get_defconfig_filename(self):
-        """Returns the name of the defconfig file, which is the first existing
-        file in the list given in a symbol having 'option defconfig_list' set.
-        $-references to symbols will be expanded ("$FOO bar" -> "foo bar" if
-        FOO has the value "foo"). Returns None in case of no defconfig file.
-        Setting 'option defconfig_list' on multiple symbols currently results
-        in undefined behavior.
-
-        If the environment variable 'srctree' was set when the Config was
-        created, get_defconfig_filename() will first look relative to that
-        directory before looking in the current directory; see
-        Config.__init__().
-
-        WARNING: A wart here is that scripts/kconfig/Makefile sometimes uses
-        the --defconfig=<defconfig> option when calling the C implementation of
-        e.g. 'make defconfig'. This option overrides the 'option
-        defconfig_list' symbol, meaning the result from
-        get_defconfig_filename() might not match what 'make defconfig' would
-        use. That probably ought to be worked around somehow, so that this
-        function always gives the "expected" result."""
-        if self.defconfig_sym is None:
-            return None
-        for filename, cond_expr in self.defconfig_sym.def_exprs:
-            if self._eval_expr(cond_expr) == "y":
-                filename = self._expand_sym_refs(filename)
-                # We first look in $srctree. os.path.join() won't work here as
-                # an absolute path in filename would override $srctree.
-                srctree_filename = os.path.normpath(self.srctree + "/" +
-                                                    filename)
-                if os.path.exists(srctree_filename):
-                    return srctree_filename
-                if os.path.exists(filename):
-                    return filename
         return None
 
-    def get_symbol(self, name):
-        """Returns the symbol with name 'name', or None if no such symbol
-        appears in the configuration. An alternative shorthand is conf[name],
-        where conf is a Config instance, though that will instead raise
-        KeyError if the symbol does not exist."""
-        return self.syms.get(name)
-
-    def __getitem__(self, name):
-        """Returns the symbol with name 'name'. Raises KeyError if the symbol
-        does not appear in the configuration."""
-        return self.syms[name]
-
-    def get_symbols(self, all_symbols=True):
-        """Returns a list of symbols from the configuration. An alternative for
-        iterating over all defined symbols (in the order of definition) is
-
-        for sym in config:
-            ...
-
-        which relies on Config implementing __iter__() and is equivalent to
-
-        for sym in config.get_symbols(False):
-            ...
-
-        all_symbols (default: True): If True, all symbols -- including special
-           and undefined symbols -- will be included in the result, in an
-           undefined order. If False, only symbols actually defined and not
-           merely referred to in the configuration will be included in the
-           result, and will appear in the order that they are defined within
-           the Kconfig configuration files."""
-        return list(self.syms.values()) if all_symbols else self.kconfig_syms
-
-    def __iter__(self):
-        """Convenience function for iterating over the set of all defined
-        symbols in the configuration, used like
-
-        for sym in conf:
-            ...
-
-        The iteration happens in the order of definition within the Kconfig
-        configuration files. Symbols only referred to but not defined will not
-        be included, nor will the special symbols n, m, and y. If you want to
-        include such symbols as well, see config.get_symbols()."""
-        return iter(self.kconfig_syms)
-
-    def get_choices(self):
-        """Returns a list containing all choice statements in the
-        configuration, in the order they appear in the Kconfig files."""
-        return self.choices
-
-    def get_menus(self):
-        """Returns a list containing all menus in the configuration, in the
-        order they appear in the Kconfig files."""
-        return self.menus
-
-    def get_comments(self):
-        """Returns a list containing all comments in the configuration, in the
-        order they appear in the Kconfig files."""
-        return self.comments
-
-    def get_top_level_items(self):
-        """Returns a list containing the items (symbols, menus, choices, and
-        comments) at the top level of the configuration -- that is, all items
-        that do not appear within a menu or choice. The items appear in the
-        same order as within the configuration."""
-        return self.top_block
-
-    def load_config(self, filename, replace=True):
-        """Loads symbol values from a file in the familiar .config format.
-        Equivalent to calling Symbol.set_user_value() to set each of the
-        values.
-
-        "# CONFIG_FOO is not set" within a .config file is treated specially
-        and sets the user value of FOO to 'n'. The C implementation works the
-        same way.
-
-        filename: The .config file to load. $-references to existing
-          environment variables will be expanded. For scripts to work even when
-          an alternative build directory is used with the Linux kernel, you
-          need to refer to the top-level kernel directory with "$srctree".
-
-        replace (default: True): True if the configuration should replace the
-           old configuration; False if it should add to it.
-
-        Returns a list or warnings (hopefully empty)
+    def load_config(self, filename=None, replace=True, verbose=None):
         """
+        Loads symbol values from a file in the .config format. Equivalent to
+        calling Symbol.set_value() to set each of the values.
 
-        self._warnings = []
-        # Regular expressions for parsing .config files
-        _set_re_match = re.compile(r"{}(\w+)=(.*)".format(self.config_prefix)).match
-        _unset_re_match = re.compile(r"# {}(\w+) is not set".format(self.config_prefix)).match
+        "# CONFIG_FOO is not set" within a .config file sets the user value of
+        FOO to n. The C tools work the same way.
 
-        # Put this first so that a missing file doesn't screw up our state
-        filename = os.path.expandvars(filename)
-        line_feeder = _FileFeed(filename)
+        For each symbol, the Symbol.user_value attribute holds the value the
+        symbol was assigned in the .config file (if any). The user value might
+        differ from Symbol.str/tri_value if there are unsatisfied dependencies.
 
-        self.config_filename = filename
+        Calling this function also updates the Kconfig.missing_syms attribute
+        with a list of all assignments to undefined symbols within the
+        configuration file. Kconfig.missing_syms is cleared if 'replace' is
+        True, and appended to otherwise. See the documentation for
+        Kconfig.missing_syms as well.
 
-        #
-        # Read header
-        #
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
 
-        def is_header_line(line):
-            return line is not None and line.startswith("#") and \
-                   not _unset_re_match(line)
+        filename (default: None):
+          Path to load configuration from (a string). Respects $srctree if set
+          (see the class documentation).
 
-        self.config_header = None
+          If 'filename' is None (the default), the configuration file to load
+          (if any) is calculated automatically, giving the behavior you'd
+          usually want:
 
-        line = line_feeder.peek_next()
-        if is_header_line(line):
-            self.config_header = ""
-            while is_header_line(line_feeder.peek_next()):
-                self.config_header += line_feeder.get_next()[1:]
-            # Remove trailing newline
-            if self.config_header.endswith("\n"):
-                self.config_header = self.config_header[:-1]
+            1. If the KCONFIG_CONFIG environment variable is set, it gives the
+               path to the configuration file to load. Otherwise, ".config" is
+               used. See standard_config_filename().
 
-        #
-        # Read assignments. Hotspot for some workloads.
-        #
+            2. If the path from (1.) doesn't exist, the configuration file
+               given by kconf.defconfig_filename is loaded instead, which is
+               derived from the 'option defconfig_list' symbol.
 
-        def warn_override(filename, linenr, name, old_user_val, new_user_val):
-            self._warn('overriding the value of {0}. '
-                       'Old value: "{1}", new value: "{2}".'
-                       .format(name, old_user_val, new_user_val),
-                       filename, linenr)
+            3. If (1.) and (2.) fail to find a configuration file to load, no
+               configuration file is loaded, and symbols retain their current
+               values (e.g., their default values). This is not an error.
+
+           See the return value as well.
+
+        replace (default: True):
+          If True, all existing user values will be cleared before loading the
+          .config. Pass False to merge configurations.
+
+        verbose (default: None):
+          Limited backwards compatibility to prevent crashes. A warning is
+          printed if anything but None is passed.
+
+          Prior to Kconfiglib 12.0.0, this option enabled printing of messages
+          to stdout when 'filename' was None. A message is (always) returned
+          now instead, which is more flexible.
+
+          Will probably be removed in some future version.
+
+        Returns a string with a message saying which file got loaded (or
+        possibly that no file got loaded, when 'filename' is None). This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.load_config()). The returned message distinguishes between
+        loading (replace == True) and merging (replace == False).
+        """
+        if verbose is not None:
+            _warn_verbose_deprecated("load_config")
+
+        msg = None
+        if filename is None:
+            filename = standard_config_filename()
+            if not exists(filename) and \
+               not exists(join(self.srctree, filename)):
+                defconfig = self.defconfig_filename
+                if defconfig is None:
+                    return "Using default symbol values (no '{}')" \
+                           .format(filename)
+
+                msg = " default configuration '{}' (no '{}')" \
+                      .format(defconfig, filename)
+                filename = defconfig
+
+        if not msg:
+            msg = " configuration '{}'".format(filename)
+
+        # Disable the warning about assigning to symbols without prompts. This
+        # is normal and expected within a .config file.
+        self._warn_assign_no_prompt = False
+
+        # This stub only exists to make sure _warn_assign_no_prompt gets
+        # reenabled
+        try:
+            self._load_config(filename, replace)
+        except UnicodeDecodeError as e:
+            _decoding_error(e, filename)
+        finally:
+            self._warn_assign_no_prompt = True
+
+        return ("Loaded" if replace else "Merged") + msg
+
+    def _load_config(self, filename, replace):
+        with self._open_config(filename) as f:
+            if replace:
+                self.missing_syms = []
+
+                # If we're replacing the configuration, keep track of which
+                # symbols and choices got set so that we can unset the rest
+                # later. This avoids invalidating everything and is faster.
+                # Another benefit is that invalidation must be rock solid for
+                # it to work, making it a good test.
+
+                for sym in self.unique_defined_syms:
+                    sym._was_set = False
+
+                for choice in self.unique_choices:
+                    choice._was_set = False
+
+            # Small optimizations
+            set_match = self._set_match
+            unset_match = self._unset_match
+            get_sym = self.syms.get
+
+            for linenr, line in enumerate(f, 1):
+                # The C tools ignore trailing whitespace
+                line = line.rstrip()
+
+                match = set_match(line)
+                if match:
+                    name, val = match.groups()
+                    sym = get_sym(name)
+                    if not sym or not sym.nodes:
+                        self._undef_assign(name, val, filename, linenr)
+                        continue
+
+                    if sym.orig_type in _BOOL_TRISTATE:
+                        # The C implementation only checks the first character
+                        # to the right of '=', for whatever reason
+                        if not (sym.orig_type is BOOL
+                                and val.startswith(("y", "n")) or
+                                sym.orig_type is TRISTATE
+                                and val.startswith(("y", "m", "n"))):
+                            self._warn("'{}' is not a valid value for the {} "
+                                       "symbol {}. Assignment ignored."
+                                       .format(val, TYPE_TO_STR[sym.orig_type],
+                                               _name_and_loc(sym)),
+                                       filename, linenr)
+                            continue
+
+                        val = val[0]
+
+                        if sym.choice and val != "n":
+                            # During .config loading, we infer the mode of the
+                            # choice from the kind of values that are assigned
+                            # to the choice symbols
+
+                            prev_mode = sym.choice.user_value
+                            if prev_mode is not None and \
+                               TRI_TO_STR[prev_mode] != val:
+
+                                self._warn("both m and y assigned to symbols "
+                                           "within the same choice",
+                                           filename, linenr)
+
+                            # Set the choice's mode
+                            sym.choice.set_value(val)
+
+                    elif sym.orig_type is STRING:
+                        match = _conf_string_match(val)
+                        if not match:
+                            self._warn("malformed string literal in "
+                                       "assignment to {}. Assignment ignored."
+                                       .format(_name_and_loc(sym)),
+                                       filename, linenr)
+                            continue
+
+                        val = unescape(match.group(1))
+
+                else:
+                    match = unset_match(line)
+                    if not match:
+                        # Print a warning for lines that match neither
+                        # set_match() nor unset_match() and that are not blank
+                        # lines or comments. 'line' has already been
+                        # rstrip()'d, so blank lines show up as "" here.
+                        if line and not line.lstrip().startswith("#"):
+                            self._warn("ignoring malformed line '{}'"
+                                       .format(line),
+                                       filename, linenr)
+
+                        continue
+
+                    name = match.group(1)
+                    sym = get_sym(name)
+                    if not sym or not sym.nodes:
+                        self._undef_assign(name, "n", filename, linenr)
+                        continue
+
+                    if sym.orig_type not in _BOOL_TRISTATE:
+                        continue
+
+                    val = "n"
+
+                # Done parsing the assignment. Set the value.
+
+                if sym._was_set:
+                    self._assigned_twice(sym, val, filename, linenr)
+
+                sym.set_value(val)
 
-        # Invalidate everything to keep things simple. It might be possible to
-        # improve performance for the case where multiple configurations are
-        # loaded by only invalidating a symbol (and its dependent symbols) if
-        # the new user value differs from the old. One complication would be
-        # that symbols not mentioned in the .config must lose their user value
-        # when replace = True, which is the usual case.
         if replace:
-            self.unset_user_values()
+            # If we're replacing the configuration, unset the symbols that
+            # didn't get set
+
+            for sym in self.unique_defined_syms:
+                if not sym._was_set:
+                    sym.unset_value()
+
+            for choice in self.unique_choices:
+                if not choice._was_set:
+                    choice.unset_value()
+
+    def _undef_assign(self, name, val, filename, linenr):
+        # Called for assignments to undefined symbols during .config loading
+
+        self.missing_syms.append((name, val))
+        if self.warn_assign_undef:
+            self._warn(
+                "attempt to assign the value '{}' to the undefined symbol {}"
+                .format(val, name), filename, linenr)
+
+    def _assigned_twice(self, sym, new_val, filename, linenr):
+        # Called when a symbol is assigned more than once in a .config file
+
+        # Use strings for bool/tristate user values in the warning
+        if sym.orig_type in _BOOL_TRISTATE:
+            user_val = TRI_TO_STR[sym.user_value]
         else:
-            self._invalidate_all()
+            user_val = sym.user_value
 
+        msg = '{} set more than once. Old value "{}", new value "{}".'.format(
+            _name_and_loc(sym), user_val, new_val)
+
+        if user_val == new_val:
+            if self.warn_assign_redun:
+                self._warn(msg, filename, linenr)
+        elif self.warn_assign_override:
+            self._warn(msg, filename, linenr)
+
+    def write_autoconf(self, filename,
+                       header="/* Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib) */\n"):
+        r"""
+        Writes out symbol values as a C header file, matching the format used
+        by include/generated/autoconf.h in the kernel.
+
+        The ordering of the #defines matches the one generated by
+        write_config(). The order in the C implementation depends on the hash
+        table implementation as of writing, and so won't match.
+
+        If 'filename' exists and its contents is identical to what would get
+        written out, it is left untouched. This avoids updating file metadata
+        like the modification time and possibly triggering redundant work in
+        build tools.
+
+        filename:
+          Self-explanatory.
+
+        header (default: "/* Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib) */\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want it enclosed in '/* */' to make it a C comment,
+          and include a final terminating newline.
+        """
+        self._write_if_changed(filename, self._autoconf_contents(header))
+
+    def _autoconf_contents(self, header):
+        # write_autoconf() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
+
+        # "".join()ed later
+        chunks = [header]
+        add = chunks.append
+
+        for sym in self.unique_defined_syms:
+            # _write_to_conf is determined when the value is calculated. This
+            # is a hidden function call due to property magic.
+            #
+            # Note: In client code, you can check if sym.config_string is empty
+            # instead, to avoid accessing the internal _write_to_conf variable
+            # (though it's likely to keep working).
+            val = sym.str_value
+            if not sym._write_to_conf:
+                continue
+
+            if sym.orig_type in _BOOL_TRISTATE:
+                if val == "y":
+                    add("#define {}{} 1\n"
+                        .format(self.config_prefix, sym.name))
+                elif val == "m":
+                    add("#define {}{}_MODULE 1\n"
+                        .format(self.config_prefix, sym.name))
+
+            elif sym.orig_type is STRING:
+                add('#define {}{} "{}"\n'
+                    .format(self.config_prefix, sym.name, escape(val)))
+
+            else:  # sym.orig_type in _INT_HEX:
+                if sym.orig_type is HEX and \
+                   not val.startswith(("0x", "0X")):
+                    val = "0x" + val
+
+                add("#define {}{} {}\n"
+                    .format(self.config_prefix, sym.name, val))
+
+        return "".join(chunks)
+
+    def write_config(self, filename=None,
+                     header="# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n",
+                     save_old=True, verbose=None):
+        r"""
+        Writes out symbol values in the .config format. The format matches the
+        C implementation, including ordering.
+
+        Symbols appear in the same order in generated .config files as they do
+        in the Kconfig files. For symbols defined in multiple locations, a
+        single assignment is written out corresponding to the first location
+        where the symbol is defined.
+
+        See the 'Intro to symbol values' section in the module docstring to
+        understand which symbols get written out.
+
+        If 'filename' exists and its contents is identical to what would get
+        written out, it is left untouched. This avoids updating file metadata
+        like the modification time and possibly triggering redundant work in
+        build tools.
+
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
+
+        filename (default: None):
+          Filename to save configuration to (a string).
+
+          If None (the default), the filename in the environment variable
+          KCONFIG_CONFIG is used if set, and ".config" otherwise. See
+          standard_config_filename().
+
+        header (default: "# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want each line to start with '#' to make it a comment,
+          and include a final terminating newline.
+
+        save_old (default: True):
+          If True and <filename> already exists, a copy of it will be saved to
+          <filename>.old in the same directory before the new configuration is
+          written.
+
+          Errors are silently ignored if <filename>.old cannot be written (e.g.
+          due to being a directory, or <filename> being something like
+          /dev/null).
+
+        verbose (default: None):
+          Limited backwards compatibility to prevent crashes. A warning is
+          printed if anything but None is passed.
+
+          Prior to Kconfiglib 12.0.0, this option enabled printing of messages
+          to stdout when 'filename' was None. A message is (always) returned
+          now instead, which is more flexible.
+
+          Will probably be removed in some future version.
+
+        Returns a string with a message saying which file got saved. This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.write_config()).
+        """
+        if verbose is not None:
+            _warn_verbose_deprecated("write_config")
+
+        if filename is None:
+            filename = standard_config_filename()
+
+        contents = self._config_contents(header)
+        if self._contents_eq(filename, contents):
+            return "No change to '{}'".format(filename)
+
+        if save_old:
+            _save_old(filename)
+
+        with self._open(filename, "w") as f:
+            f.write(contents)
+
+        return "Configuration saved to '{}'".format(filename)
+
+    def _config_contents(self, header):
+        # write_config() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
+        #
+        # More memory friendly would be to 'yield' the strings and
+        # "".join(_config_contents()), but it was a bit slower on my system.
+
+        # node_iter() was used here before commit 3aea9f7 ("Add '# end of
+        # <menu>' after menus in .config"). Those comments get tricky to
+        # implement with it.
+
+        for sym in self.unique_defined_syms:
+            sym._visited = False
+
+        # Did we just print an '# end of ...' comment?
+        after_end_comment = False
+
+        # "".join()ed later
+        chunks = [header]
+        add = chunks.append
+
+        node = self.top_node
         while 1:
-            line = line_feeder.get_next()
-            if line is None:
-                return self._warnings
+            # Jump to the next node with an iterative tree walk
+            if node.list:
+                node = node.list
+            elif node.next:
+                node = node.next
+            else:
+                while node.parent:
+                    node = node.parent
 
-            line = line.rstrip()
+                    # Add a comment when leaving visible menus
+                    if node.item is MENU and expr_value(node.dep) and \
+                       expr_value(node.visibility) and \
+                       node is not self.top_node:
+                        add("# end of {}\n".format(node.prompt[0]))
+                        after_end_comment = True
 
-            set_match = _set_re_match(line)
-            if set_match:
-                name, val = set_match.groups()
+                    if node.next:
+                        node = node.next
+                        break
+                else:
+                    # No more nodes
+                    return "".join(chunks)
 
-                if val.startswith('"'):
-                    if len(val) < 2 or val[-1] != '"':
-                        _parse_error(line, "malformed string literal",
-                                     line_feeder.filename, line_feeder.linenr)
-                    # Strip quotes and remove escapings. The unescaping
-                    # procedure should be safe since " can only appear as \"
-                    # inside the string.
-                    val = val[1:-1].replace('\\"', '"').replace("\\\\", "\\")
+            # Generate configuration output for the node
 
+            item = node.item
+
+            if item.__class__ is Symbol:
+                if item._visited:
+                    continue
+                item._visited = True
+
+                conf_string = item.config_string
+                if not conf_string:
+                    continue
+
+                if after_end_comment:
+                    # Add a blank line before the first symbol printed after an
+                    # '# end of ...' comment
+                    after_end_comment = False
+                    add("\n")
+                add(conf_string)
+
+            elif expr_value(node.dep) and \
+                 ((item is MENU and expr_value(node.visibility)) or
+                  item is COMMENT):
+
+                add("\n#\n# {}\n#\n".format(node.prompt[0]))
+                after_end_comment = False
+
+    def write_min_config(self, filename,
+                         header="# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+        """
+        Writes out a "minimal" configuration file, omitting symbols whose value
+        matches their default value. The format matches the one produced by
+        'make savedefconfig'.
+
+        The resulting configuration file is incomplete, but a complete
+        configuration can be derived from it by loading it. Minimal
+        configuration files can serve as a more manageable configuration format
+        compared to a "full" .config file, especially when configurations files
+        are merged or edited by hand.
+
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
+
+        filename:
+          Self-explanatory.
+
+        header (default: "# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want each line to start with '#' to make it a comment,
+          and include a final terminating newline.
+
+        Returns a string with a message saying which file got saved. This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.write_min_config()).
+        """
+        contents = self._min_config_contents(header)
+        if self._contents_eq(filename, contents):
+            return "No change to '{}'".format(filename)
+
+        with self._open(filename, "w") as f:
+            f.write(contents)
+
+        return "Minimal configuration saved to '{}'".format(filename)
+
+    def _min_config_contents(self, header):
+        # write_min_config() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
+
+        chunks = [header]
+        add = chunks.append
+
+        for sym in self.unique_defined_syms:
+            # Skip symbols that cannot be changed. Only check
+            # non-choice symbols, as selects don't affect choice
+            # symbols.
+            if not sym.choice and \
+               sym.visibility <= expr_value(sym.rev_dep):
+                continue
+
+            # Skip symbols whose value matches their default
+            if sym.str_value == sym._str_default():
+                continue
+
+            # Skip symbols that would be selected by default in a
+            # choice, unless the choice is optional or the symbol type
+            # isn't bool (it might be possible to set the choice mode
+            # to n or the symbol to m in those cases).
+            if sym.choice and \
+               not sym.choice.is_optional and \
+               sym.choice._selection_from_defaults() is sym and \
+               sym.orig_type is BOOL and \
+               sym.tri_value == 2:
+                continue
+
+            add(sym.config_string)
+
+        return "".join(chunks)
+
+    def sync_deps(self, path):
+        """
+        Creates or updates a directory structure that can be used to avoid
+        doing a full rebuild whenever the configuration is changed, mirroring
+        include/config/ in the kernel.
+
+        This function is intended to be called during each build, before
+        compiling source files that depend on configuration symbols.
+
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
+
+        path:
+          Path to directory
+
+        sync_deps(path) does the following:
+
+          1. If the directory <path> does not exist, it is created.
+
+          2. If <path>/auto.conf exists, old symbol values are loaded from it,
+             which are then compared against the current symbol values. If a
+             symbol has changed value (would generate different output in
+             autoconf.h compared to before), the change is signaled by
+             touch'ing a file corresponding to the symbol.
+
+             The first time sync_deps() is run on a directory, <path>/auto.conf
+             won't exist, and no old symbol values will be available. This
+             logically has the same effect as updating the entire
+             configuration.
+
+             The path to a symbol's file is calculated from the symbol's name
+             by replacing all '_' with '/' and appending '.h'. For example, the
+             symbol FOO_BAR_BAZ gets the file <path>/foo/bar/baz.h, and FOO
+             gets the file <path>/foo.h.
+
+             This scheme matches the C tools. The point is to avoid having a
+             single directory with a huge number of files, which the underlying
+             filesystem might not handle well.
+
+          3. A new auto.conf with the current symbol values is written, to keep
+             track of them for the next build.
+
+             If auto.conf exists and its contents is identical to what would
+             get written out, it is left untouched. This avoids updating file
+             metadata like the modification time and possibly triggering
+             redundant work in build tools.
+
+
+        The last piece of the puzzle is knowing what symbols each source file
+        depends on. Knowing that, dependencies can be added from source files
+        to the files corresponding to the symbols they depends on. The source
+        file will then get recompiled (only) when the symbol value changes
+        (provided sync_deps() is run first during each build).
+
+        The tool in the kernel that extracts symbol dependencies from source
+        files is scripts/basic/fixdep.c. Missing symbol files also correspond
+        to "not changed", which fixdep deals with by using the $(wildcard) Make
+        function when adding symbol prerequisites to source files.
+
+        In case you need a different scheme for your project, the sync_deps()
+        implementation can be used as a template.
+        """
+        if not exists(path):
+            os.mkdir(path, 0o755)
+
+        # Load old values from auto.conf, if any
+        self._load_old_vals(path)
+
+        for sym in self.unique_defined_syms:
+            # _write_to_conf is determined when the value is calculated. This
+            # is a hidden function call due to property magic.
+            #
+            # Note: In client code, you can check if sym.config_string is empty
+            # instead, to avoid accessing the internal _write_to_conf variable
+            # (though it's likely to keep working).
+            val = sym.str_value
+
+            # n tristate values do not get written to auto.conf and autoconf.h,
+            # making a missing symbol logically equivalent to n
+
+            if sym._write_to_conf:
+                if sym._old_val is None and \
+                   sym.orig_type in _BOOL_TRISTATE and \
+                   val == "n":
+                    # No old value (the symbol was missing or n), new value n.
+                    # No change.
+                    continue
+
+                if val == sym._old_val:
+                    # New value matches old. No change.
+                    continue
+
+            elif sym._old_val is None:
+                # The symbol wouldn't appear in autoconf.h (because
+                # _write_to_conf is false), and it wouldn't have appeared in
+                # autoconf.h previously either (because it didn't appear in
+                # auto.conf). No change.
+                continue
+
+            # 'sym' has a new value. Flag it.
+            _touch_dep_file(path, sym.name)
+
+        # Remember the current values as the "new old" values.
+        #
+        # This call could go anywhere after the call to _load_old_vals(), but
+        # putting it last means _sync_deps() can be safely rerun if it fails
+        # before this point.
+        self._write_old_vals(path)
+
+    def _load_old_vals(self, path):
+        # Loads old symbol values from auto.conf into a dedicated
+        # Symbol._old_val field. Mirrors load_config().
+        #
+        # The extra field could be avoided with some trickery involving dumping
+        # symbol values and restoring them later, but this is simpler and
+        # faster. The C tools also use a dedicated field for this purpose.
+
+        for sym in self.unique_defined_syms:
+            sym._old_val = None
+
+        try:
+            auto_conf = self._open(join(path, "auto.conf"), "r")
+        except EnvironmentError as e:
+            if e.errno == errno.ENOENT:
+                # No old values
+                return
+            raise
+
+        with auto_conf as f:
+            for line in f:
+                match = self._set_match(line)
+                if not match:
+                    # We only expect CONFIG_FOO=... (and possibly a header
+                    # comment) in auto.conf
+                    continue
+
+                name, val = match.groups()
                 if name in self.syms:
                     sym = self.syms[name]
-                    if sym.user_val is not None:
-                        warn_override(line_feeder.filename, line_feeder.linenr,
-                                      name, sym.user_val, val)
 
-                    if sym.is_choice_sym:
-                        user_mode = sym.parent.user_mode
-                        if user_mode is not None and user_mode != val:
-                            self._warn("assignment to {0} changes mode of "
-                                       'containing choice from "{1}" to "{2}".'
-                                       .format(name, val, user_mode),
-                                       line_feeder.filename,
-                                       line_feeder.linenr)
+                    if sym.orig_type is STRING:
+                        match = _conf_string_match(val)
+                        if not match:
+                            continue
+                        val = unescape(match.group(1))
 
-                    sym._set_user_value_no_invalidate(val, True)
+                    self.syms[name]._old_val = val
                 else:
-                    if self.print_undef_assign:
-                        _stderr_msg('note: attempt to assign the value "{0}" '
-                                    "to the undefined symbol {1}."
-                                    .format(val, name),
-                                    line_feeder.filename, line_feeder.linenr)
+                    # Flag that the symbol no longer exists, in
+                    # case something still depends on it
+                    _touch_dep_file(path, name)
+
+    def _write_old_vals(self, path):
+        # Helper for writing auto.conf. Basically just a simplified
+        # write_config() that doesn't write any comments (including
+        # '# CONFIG_FOO is not set' comments). The format matches the C
+        # implementation, though the ordering is arbitrary there (depends on
+        # the hash table implementation).
+        #
+        # A separate helper function is neater than complicating write_config()
+        # by passing a flag to it, plus we only need to look at symbols here.
+
+        self._write_if_changed(
+            os.path.join(path, "auto.conf"),
+            self._old_vals_contents())
+
+    def _old_vals_contents(self):
+        # _write_old_vals() helper. Returns the contents to write as a string.
+
+        # Temporary list instead of generator makes this a bit faster
+        return "".join([
+            sym.config_string for sym in self.unique_defined_syms
+                if not (sym.orig_type in _BOOL_TRISTATE and not sym.tri_value)
+        ])
+
+    def node_iter(self, unique_syms=False):
+        """
+        Returns a generator for iterating through all MenuNode's in the Kconfig
+        tree. The iteration is done in Kconfig definition order (each node is
+        visited before its children, and the children of a node are visited
+        before the next node).
+
+        The Kconfig.top_node menu node is skipped. It contains an implicit menu
+        that holds the top-level items.
+
+        As an example, the following code will produce a list equal to
+        Kconfig.defined_syms:
+
+          defined_syms = [node.item for node in kconf.node_iter()
+                          if isinstance(node.item, Symbol)]
+
+        unique_syms (default: False):
+          If True, only the first MenuNode will be included for symbols defined
+          in multiple locations.
+
+          Using kconf.node_iter(True) in the example above would give a list
+          equal to unique_defined_syms.
+        """
+        if unique_syms:
+            for sym in self.unique_defined_syms:
+                sym._visited = False
+
+        node = self.top_node
+        while 1:
+            # Jump to the next node with an iterative tree walk
+            if node.list:
+                node = node.list
+            elif node.next:
+                node = node.next
             else:
-                unset_match = _unset_re_match(line)
-                if unset_match:
-                    name = unset_match.group(1)
-                    if name in self.syms:
-                        sym = self.syms[name]
-                        if sym.user_val is not None:
-                            warn_override(line_feeder.filename,
-                                          line_feeder.linenr,
-                                          name, sym.user_val, "n")
+                while node.parent:
+                    node = node.parent
+                    if node.next:
+                        node = node.next
+                        break
+                else:
+                    # No more nodes
+                    return
 
-                        sym._set_user_value_no_invalidate("n", True)
+            if unique_syms and node.item.__class__ is Symbol:
+                if node.item._visited:
+                    continue
+                node.item._visited = True
 
-    def write_config(self, filename, header=None):
-        """Writes out symbol values in the familiar .config format.
+            yield node
 
-        Kconfiglib makes sure the format matches what the C implementation
-        would generate, down to whitespace. This eases testing.
+    def eval_string(self, s):
+        """
+        Returns the tristate value of the expression 's', represented as 0, 1,
+        and 2 for n, m, and y, respectively. Raises KconfigError on syntax
+        errors. Warns if undefined symbols are referenced.
 
-        filename: The filename under which to save the configuration.
+        As an example, if FOO and BAR are tristate symbols at least one of
+        which has the value y, then eval_string("y && (FOO || BAR)") returns
+        2 (y).
 
-        header (default: None): A textual header that will appear at the
-           beginning of the file, with each line commented out automatically.
-           None means no header."""
+        To get the string value of non-bool/tristate symbols, use
+        Symbol.str_value. eval_string() always returns a tristate value, and
+        all non-bool/tristate symbols have the tristate value 0 (n).
 
-        for sym in self.syms_iter():
-            sym.already_written = False
+        The expression parsing is consistent with how parsing works for
+        conditional ('if ...') expressions in the configuration, and matches
+        the C implementation. m is rewritten to 'm && MODULES', so
+        eval_string("m") will return 0 (n) unless modules are enabled.
+        """
+        # The parser is optimized to be fast when parsing Kconfig files (where
+        # an expression can never appear at the beginning of a line). We have
+        # to monkey-patch things a bit here to reuse it.
 
-        with open(filename, "w") as f:
-            # Write header
-            if header is not None:
-                f.write(_comment(header) + "\n")
+        self.filename = None
 
-            # Build and write configuration
-            conf_strings = []
-            _make_block_conf(self.top_block, conf_strings.append)
-            f.write("\n".join(conf_strings) + "\n")
+        self._tokens = self._tokenize("if " + s)
+        # Strip "if " to avoid giving confusing error messages
+        self._line = s
+        self._tokens_i = 1  # Skip the 'if' token
 
-    def eval(self, s):
-        """Returns the value of the expression 's' -- where 's' is represented
-        as a string -- in the context of the configuration. Raises
-        Kconfig_Syntax_Error if syntax errors are detected in 's'.
+        return expr_value(self._expect_expr_and_eol())
 
-        For example, if FOO and BAR are tristate symbols at least one of which
-        has the value "y", then config.eval("y && (FOO || BAR)") => "y"
+    def unset_values(self):
+        """
+        Removes any user values from all symbols, as if Kconfig.load_config()
+        or Symbol.set_value() had never been called.
+        """
+        self._warn_assign_no_prompt = False
+        try:
+            # set_value() already rejects undefined symbols, and they don't
+            # need to be invalidated (because their value never changes), so we
+            # can just iterate over defined symbols
+            for sym in self.unique_defined_syms:
+                sym.unset_value()
 
-        This function always yields a tristate value. To get the value of
-        non-bool, non-tristate symbols, use Symbol.get_value().
+            for choice in self.unique_choices:
+                choice.unset_value()
+        finally:
+            self._warn_assign_no_prompt = True
 
-        The result of this function is consistent with how evaluation works for
-        conditional expressions in the configuration as well as in the C
-        implementation. "m" and m are rewritten as '"m" && MODULES' and 'm &&
-        MODULES', respectively, and a result of "m" will get promoted to "y" if
-        we're running without modules.
+    def enable_warnings(self):
+        """
+        Do 'Kconfig.warn = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn = True
 
-        Syntax checking is somewhat lax, partly to be compatible with lax
-        parsing in the C implementation."""
-        return self._eval_expr(self._parse_expr(self._tokenize(s, True), # Feed
-                                                None, # Current symbol/choice
-                                                s))   # line
+    def disable_warnings(self):
+        """
+        Do 'Kconfig.warn = False' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn = False
 
-    def unset_user_values(self):
-        """Resets the values of all symbols, as if Config.load_config() or
-        Symbol.set_user_value() had never been called."""
-        for sym in self.syms_iter():
-            sym._unset_user_value_no_recursive_invalidate()
+    def enable_stderr_warnings(self):
+        """
+        Do 'Kconfig.warn_to_stderr = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_to_stderr = True
 
-    def set_print_warnings(self, print_warnings):
-        """Determines whether warnings related to this configuration (for
-        things like attempting to assign illegal values to symbols with
-        Symbol.set_user_value()) should be printed to stderr.
+    def disable_stderr_warnings(self):
+        """
+        Do 'Kconfig.warn_to_stderr = False' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_to_stderr = False
 
-        print_warnings: True if warnings should be printed."""
-        self.print_warnings = print_warnings
+    def enable_undef_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_undef = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_assign_undef = True
 
-    def set_print_undef_assign(self, print_undef_assign):
-        """Determines whether informational messages related to assignments to
-        undefined symbols should be printed to stderr for this configuration.
+    def disable_undef_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_undef = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_undef = False
 
-        print_undef_assign: If True, such messages will be printed."""
-        self.print_undef_assign = print_undef_assign
+    def enable_override_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_override = True' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_override = True
 
-    def __str__(self):
-        """Returns a string containing various information about the Config."""
-        return _lines("Configuration",
-                      "File                                   : " +
-                        self.filename,
-                      "Base directory                         : " +
-                        self.base_dir,
-                      "Value of $ARCH at creation time        : " +
-                        ("(not set)" if self.arch is None else self.arch),
-                      "Value of $SRCARCH at creation time     : " +
-                        ("(not set)" if self.srcarch is None else
-                                        self.srcarch),
-                      "Source tree (derived from $srctree;",
-                      "defaults to '.' if $srctree isn't set) : " +
-                        self.srctree,
-                      "Most recently loaded .config           : " +
-                        ("(no .config loaded)"
-                          if self.config_filename is None else
-                             self.config_filename),
-                      "Print warnings                         : " +
-                        BOOL_STR[self.print_warnings],
-                      "Print assignments to undefined symbols : " +
-                        BOOL_STR[self.print_undef_assign])
+    def disable_override_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_override = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_override = False
+
+    def enable_redun_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_redun = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_assign_redun = True
+
+    def disable_redun_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_redun = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_redun = False
+
+    def __repr__(self):
+        """
+        Returns a string with information about the Kconfig object when it is
+        evaluated on e.g. the interactive Python prompt.
+        """
+        def status(flag):
+            return "enabled" if flag else "disabled"
+
+        return "<{}>".format(", ".join((
+            "configuration with {} symbols".format(len(self.syms)),
+            'main menu prompt "{}"'.format(self.mainmenu_text),
+            "srctree is current directory" if not self.srctree else
+                'srctree "{}"'.format(self.srctree),
+            'config symbol prefix "{}"'.format(self.config_prefix),
+            "warnings " + status(self.warn),
+            "printing of warnings to stderr " + status(self.warn_to_stderr),
+            "undef. symbol assignment warnings " +
+                status(self.warn_assign_undef),
+            "overriding symbol assignment warnings " +
+                status(self.warn_assign_override),
+            "redundant symbol assignment warnings " +
+                status(self.warn_assign_redun)
+        )))
 
     #
     # Private methods
     #
 
+
     #
-    # Kconfig parsing
+    # File reading
     #
 
-    def _parse_file(self, filename, parent, deps, visible_if_deps, block):
-        """Parses the Kconfig file 'filename'. Appends the Items in the file
-        (and any file it sources) to the list passed in the 'block' parameter.
-        See _parse_block() for the meaning of the parameters."""
-        self._parse_block(_FileFeed(filename), None, parent, deps,
-                          visible_if_deps, block)
+    def _open_config(self, filename):
+        # Opens a .config file. First tries to open 'filename', then
+        # '$srctree/filename' if $srctree was set when the configuration was
+        # loaded.
 
-    def _parse_block(self, line_feeder, end_marker, parent, deps,
-                     visible_if_deps, block):
-        """Parses a block, which is the contents of either a file or an if,
-        menu, or choice statement. Appends the Items to the list passed in the
-        'block' parameter.
+        try:
+            return self._open(filename, "r")
+        except EnvironmentError as e:
+            # This will try opening the same file twice if $srctree is unset,
+            # but it's not a big deal
+            try:
+                return self._open(join(self.srctree, filename), "r")
+            except EnvironmentError as e2:
+                # This is needed for Python 3, because e2 is deleted after
+                # the try block:
+                #
+                # https://docs.python.org/3/reference/compound_stmts.html#the-try-statement
+                e = e2
 
-        line_feeder: A _FileFeed instance feeding lines from a file. The
-          Kconfig language is line-based in practice.
+            raise _KconfigIOError(
+                e, "Could not open '{}' ({}: {}). Check that the $srctree "
+                   "environment variable ({}) is set correctly."
+                   .format(filename, errno.errorcode[e.errno], e.strerror,
+                           "set to '{}'".format(self.srctree) if self.srctree
+                               else "unset or blank"))
 
-        end_marker: The token that ends the block, e.g. T_ENDIF ("endif") for
-           ifs. None for files.
+    def _enter_file(self, filename):
+        # Jumps to the beginning of a sourced Kconfig file, saving the previous
+        # position and file object.
+        #
+        # filename:
+        #   Absolute path to file
 
-        parent: The enclosing menu or choice, or None if we're at the top
-           level.
+        # Path relative to $srctree, stored in e.g. self.filename (which makes
+        # it indirectly show up in MenuNode.filename). Equals 'filename' for
+        # absolute paths passed to 'source'.
+        if filename.startswith(self._srctree_prefix):
+            # Relative path (or a redundant absolute path to within $srctree,
+            # but it's probably fine to reduce those too)
+            rel_filename = filename[len(self._srctree_prefix):]
+        else:
+            # Absolute path
+            rel_filename = filename
 
-        deps: Dependencies from enclosing menus, choices and ifs.
+        self.kconfig_filenames.append(rel_filename)
 
-        visible_if_deps (default: None): 'visible if' dependencies from
-           enclosing menus.
+        # The parent Kconfig files are represented as a list of
+        # (<include path>, <Python 'file' object for Kconfig file>) tuples.
+        #
+        # <include path> is immutable and holds a *tuple* of
+        # (<filename>, <linenr>) tuples, giving the locations of the 'source'
+        # statements in the parent Kconfig files. The current include path is
+        # also available in Kconfig._include_path.
+        #
+        # The point of this redundant setup is to allow Kconfig._include_path
+        # to be assigned directly to MenuNode.include_path without having to
+        # copy it, sharing it wherever possible.
 
-        block: The list to add items to."""
+        # Save include path and 'file' object (via its 'readline' function)
+        # before entering the file
+        self._filestack.append((self._include_path, self._readline))
 
-        while 1:
-            # Do we already have a tokenized line that we determined wasn't
-            # part of whatever we were parsing earlier? See comment in
-            # Config.__init__().
-            if self.end_line is not None:
-                line = self.end_line
-                tokens = self.end_line_tokens
-                tokens.unget_all()
+        # _include_path is a tuple, so this rebinds the variable instead of
+        # doing in-place modification
+        self._include_path += ((self.filename, self.linenr),)
 
-                self.end_line = None
-                self.end_line_tokens = None
-            else:
-                line = line_feeder.get_next()
-                if line is None:
-                    if end_marker is not None:
-                        raise Kconfig_Syntax_Error("Unexpected end of file {0}"
-                                                 .format(line_feeder.filename))
-                    return
+        # Check for recursive 'source'
+        for name, _ in self._include_path:
+            if name == rel_filename:
+                raise KconfigError(
+                    "\n{}:{}: recursive 'source' of '{}' detected. Check that "
+                    "environment variables are set correctly.\n"
+                    "Include path:\n{}"
+                    .format(self.filename, self.linenr, rel_filename,
+                            "\n".join("{}:{}".format(name, linenr)
+                                      for name, linenr in self._include_path)))
 
-                tokens = self._tokenize(line, False, line_feeder.filename,
-                                        line_feeder.linenr)
+        try:
+            self._readline = self._open(filename, "r").readline
+        except EnvironmentError as e:
+            # We already know that the file exists
+            raise _KconfigIOError(
+                e, "{}:{}: Could not open '{}' (in '{}') ({}: {})"
+                   .format(self.filename, self.linenr, filename,
+                           self._line.strip(),
+                           errno.errorcode[e.errno], e.strerror))
 
-            t0 = tokens.get_next()
-            if t0 is None:
-                continue
+        self.filename = rel_filename
+        self.linenr = 0
 
-            # Cases are ordered roughly by frequency, which speeds things up a
-            # bit
+    def _leave_file(self):
+        # Returns from a Kconfig file to the file that sourced it. See
+        # _enter_file().
 
-            if t0 == T_CONFIG or t0 == T_MENUCONFIG:
-                # The tokenizer will automatically allocate a new Symbol object
-                # for any new names it encounters, so we don't need to worry
-                # about that here.
-                sym = tokens.get_next()
+        # Restore location from parent Kconfig file
+        self.filename, self.linenr = self._include_path[-1]
+        # Restore include path and 'file' object
+        self._readline.__self__.close()  # __self__ fetches the 'file' object
+        self._include_path, self._readline = self._filestack.pop()
 
-                # Symbols defined in multiple places get the parent of their
-                # first definition. However, for symbols whose parents are
-                # choice statements, the choice statement takes precedence.
-                if not sym.is_defined_ or isinstance(parent, Choice):
-                    sym.parent = parent
-                sym.is_defined_ = True
+    def _next_line(self):
+        # Fetches and tokenizes the next line from the current Kconfig file.
+        # Returns False at EOF and True otherwise.
 
-                self._parse_properties(line_feeder, sym, deps, visible_if_deps)
+        # We might already have tokens from parsing a line and discovering that
+        # it's part of a different construct
+        if self._reuse_tokens:
+            self._reuse_tokens = False
+            # self._tokens_i is known to be 1 here, because _parse_properties()
+            # leaves it like that when it can't recognize a line (or parses
+            # a help text)
+            return True
 
-                self.kconfig_syms.append(sym)
-                block.append(sym)
+        # readline() returns '' over and over at EOF, which we rely on for help
+        # texts at the end of files (see _line_after_help())
+        line = self._readline()
+        if not line:
+            return False
+        self.linenr += 1
 
-            elif t0 == T_SOURCE:
-                kconfig_file = tokens.get_next()
-                exp_kconfig_file = self._expand_sym_refs(kconfig_file)
-                f = os.path.join(self.base_dir, exp_kconfig_file)
-                if not os.path.exists(f):
-                    raise IOError('{0}:{1}: sourced file "{2}" (expands to '
-                                  '"{3}") not found. Perhaps base_dir '
-                                  '(argument to Config.__init__(), currently '
-                                  '"{4}") is set to the wrong value.'
-                                  .format(line_feeder.filename,
-                                          line_feeder.linenr,
-                                          kconfig_file, exp_kconfig_file,
-                                          self.base_dir))
-                # Add items to the same block
-                self._parse_file(f, parent, deps, visible_if_deps, block)
+        # Handle line joining
+        while line.endswith("\\\n"):
+            line = line[:-2] + self._readline()
+            self.linenr += 1
 
-            elif t0 == end_marker:
-                # We have reached the end of the block
-                return
+        self._tokens = self._tokenize(line)
+        # Initialize to 1 instead of 0 to factor out code from _parse_block()
+        # and _parse_properties(). They immediately fetch self._tokens[0].
+        self._tokens_i = 1
 
-            elif t0 == T_IF:
-                # If statements are treated as syntactic sugar for adding
-                # dependencies to enclosed items and do not have an explicit
-                # object representation.
+        return True
 
-                dep_expr = self._parse_expr(tokens, None, line,
-                                            line_feeder.filename,
-                                            line_feeder.linenr)
-                # Add items to the same block
-                self._parse_block(line_feeder, T_ENDIF, parent,
-                                  _make_and(dep_expr, deps),
-                                  visible_if_deps, block)
+    def _line_after_help(self, line):
+        # Tokenizes a line after a help text. This case is special in that the
+        # line has already been fetched (to discover that it isn't part of the
+        # help text).
+        #
+        # An earlier version used a _saved_line variable instead that was
+        # checked in _next_line(). This special-casing gets rid of it and makes
+        # _reuse_tokens alone sufficient to handle unget.
 
-            elif t0 == T_COMMENT:
-                comment = Comment()
-                comment.config = self
-                comment.parent = parent
-                comment.filename = line_feeder.filename
-                comment.linenr = line_feeder.linenr
-                comment.text = tokens.get_next()
+        # Handle line joining
+        while line.endswith("\\\n"):
+            line = line[:-2] + self._readline()
+            self.linenr += 1
 
-                self._parse_properties(line_feeder, comment, deps,
-                                       visible_if_deps)
+        self._tokens = self._tokenize(line)
+        self._reuse_tokens = True
 
-                self.comments.append(comment)
-                block.append(comment)
+    def _write_if_changed(self, filename, contents):
+        # Writes 'contents' into 'filename', but only if it differs from the
+        # current contents of the file.
+        #
+        # Another variant would be write a temporary file on the same
+        # filesystem, compare the files, and rename() the temporary file if it
+        # differs, but it breaks stuff like write_config("/dev/null"), which is
+        # used out there to force evaluation-related warnings to be generated.
+        # This simple version is pretty failsafe and portable.
 
-            elif t0 == T_MENU:
-                menu = Menu()
-                menu.config = self
-                menu.parent = parent
-                menu.filename = line_feeder.filename
-                menu.linenr = line_feeder.linenr
-                menu.title = tokens.get_next()
+        if not self._contents_eq(filename, contents):
+            with self._open(filename, "w") as f:
+                f.write(contents)
 
-                self._parse_properties(line_feeder, menu, deps,
-                                       visible_if_deps)
+    def _contents_eq(self, filename, contents):
+        # Returns True if the contents of 'filename' is 'contents' (a string),
+        # and False otherwise (including if 'filename' can't be opened/read)
 
-                # This needs to go before _parse_block() so that we get the
-                # proper menu ordering in the case of nested functions
-                self.menus.append(menu)
-                # Parse contents and put Items in menu.block
-                self._parse_block(line_feeder, T_ENDMENU, menu, menu.dep_expr,
-                                  _make_and(visible_if_deps,
-                                            menu.visible_if_expr),
-                                  menu.block)
+        try:
+            with self._open(filename, "r") as f:
+                # Robust re. things like encoding and line endings (mmap()
+                # trickery isn't)
+                return f.read(len(contents) + 1) == contents
+        except EnvironmentError:
+            # If the error here would prevent writing the file as well, we'll
+            # notice it later
+            return False
 
-                block.append(menu)
+    #
+    # Tokenization
+    #
+
+    def _lookup_sym(self, name):
+        # Fetches the symbol 'name' from the symbol table, creating and
+        # registering it if it does not exist. If '_parsing_kconfigs' is False,
+        # it means we're in eval_string(), and new symbols won't be registered.
+
+        if name in self.syms:
+            return self.syms[name]
+
+        sym = Symbol()
+        sym.kconfig = self
+        sym.name = name
+        sym.is_constant = False
+        sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
+
+        if self._parsing_kconfigs:
+            self.syms[name] = sym
+        else:
+            self._warn("no symbol {} in configuration".format(name))
+
+        return sym
+
+    def _lookup_const_sym(self, name):
+        # Like _lookup_sym(), for constant (quoted) symbols
+
+        if name in self.const_syms:
+            return self.const_syms[name]
+
+        sym = Symbol()
+        sym.kconfig = self
+        sym.name = name
+        sym.is_constant = True
+        sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
+
+        if self._parsing_kconfigs:
+            self.const_syms[name] = sym
+
+        return sym
+
+    def _tokenize(self, s):
+        # Parses 's', returning a None-terminated list of tokens. Registers any
+        # new symbols encountered with _lookup(_const)_sym().
+        #
+        # Tries to be reasonably speedy by processing chunks of text via
+        # regexes and string operations where possible. This is the biggest
+        # hotspot during parsing.
+        #
+        # It might be possible to rewrite this to 'yield' tokens instead,
+        # working across multiple lines. Lookback and compatibility with old
+        # janky versions of the C tools complicate things though.
+
+        self._line = s  # Used for error reporting
+
+        # Initial token on the line
+        match = _command_match(s)
+        if not match:
+            if s.isspace() or s.lstrip().startswith("#"):
+                return (None,)
+            self._parse_error("unknown token at start of line")
+
+        # Tricky implementation detail: While parsing a token, 'token' refers
+        # to the previous token. See _STRING_LEX for why this is needed.
+        token = _get_keyword(match.group(1))
+        if not token:
+            # Backwards compatibility with old versions of the C tools, which
+            # (accidentally) accepted stuff like "--help--" and "-help---".
+            # This was fixed in the C tools by commit c2264564 ("kconfig: warn
+            # of unhandled characters in Kconfig commands"), committed in July
+            # 2015, but it seems people still run Kconfiglib on older kernels.
+            if s.strip(" \t\n-") == "help":
+                return (_T_HELP, None)
+
+            # If the first token is not a keyword (and not a weird help token),
+            # we have a preprocessor variable assignment (or a bare macro on a
+            # line)
+            self._parse_assignment(s)
+            return (None,)
+
+        tokens = [token]
+        # The current index in the string being tokenized
+        i = match.end()
+
+        # Main tokenization loop (for tokens past the first one)
+        while i < len(s):
+            # Test for an identifier/keyword first. This is the most common
+            # case.
+            match = _id_keyword_match(s, i)
+            if match:
+                # We have an identifier or keyword
+
+                # Check what it is. lookup_sym() will take care of allocating
+                # new symbols for us the first time we see them. Note that
+                # 'token' still refers to the previous token.
+
+                name = match.group(1)
+                keyword = _get_keyword(name)
+                if keyword:
+                    # It's a keyword
+                    token = keyword
+                    # Jump past it
+                    i = match.end()
+
+                elif token not in _STRING_LEX:
+                    # It's a non-const symbol, except we translate n, m, and y
+                    # into the corresponding constant symbols, like the C
+                    # implementation
+
+                    if "$" in name:
+                        # Macro expansion within symbol name
+                        name, s, i = self._expand_name(s, i)
+                    else:
+                        i = match.end()
+
+                    token = self.const_syms[name] if name in STR_TO_TRI else \
+                        self._lookup_sym(name)
 
-            elif t0 == T_CHOICE:
-                name = tokens.get_next()
-                if name is None:
-                    choice = Choice()
-                    self.choices.append(choice)
                 else:
-                    # Named choice
-                    choice = self.named_choices.get(name)
-                    if choice is None:
-                        choice = Choice()
-                        choice.name = name
-                        self.named_choices[name] = choice
-                        self.choices.append(choice)
+                    # It's a case of missing quotes. For example, the
+                    # following is accepted:
+                    #
+                    #   menu unquoted_title
+                    #
+                    #   config A
+                    #       tristate unquoted_prompt
+                    #
+                    #   endmenu
+                    #
+                    # Named choices ('choice FOO') also end up here.
 
-                choice.config = self
-                choice.parent = parent
+                    if token is not _T_CHOICE:
+                        self._warn("style: quotes recommended around '{}' in '{}'"
+                                   .format(name, self._line.strip()),
+                                   self.filename, self.linenr)
 
-                choice.def_locations.append((line_feeder.filename,
-                                             line_feeder.linenr))
-
-                self._parse_properties(line_feeder, choice, deps,
-                                       visible_if_deps)
-
-                # Parse contents and put Items in choice.block
-                self._parse_block(line_feeder, T_ENDCHOICE, choice, deps,
-                                  visible_if_deps, choice.block)
-
-                choice._determine_actual_symbols()
-
-                # If no type is specified for the choice, its type is that of
-                # the first choice item with a specified type
-                if choice.type == UNKNOWN:
-                    for item in choice.actual_symbols:
-                        if item.type != UNKNOWN:
-                            choice.type = item.type
-                            break
-
-                # Each choice item of UNKNOWN type gets the type of the choice
-                for item in choice.actual_symbols:
-                    if item.type == UNKNOWN:
-                        item.type = choice.type
-
-                block.append(choice)
-
-            elif t0 == T_MAINMENU:
-                text = tokens.get_next()
-                if self.mainmenu_text is not None:
-                    self._warn("overriding 'mainmenu' text. "
-                               'Old value: "{0}", new value: "{1}".'
-                               .format(self.mainmenu_text, text),
-                               line_feeder.filename, line_feeder.linenr)
-                self.mainmenu_text = text
+                    token = name
+                    i = match.end()
 
             else:
-                _parse_error(line, "unrecognized construct",
-                             line_feeder.filename, line_feeder.linenr)
+                # Neither a keyword nor a non-const symbol
 
-    def _parse_properties(self, line_feeder, stmt, deps, visible_if_deps):
-        """Parsing of properties for symbols, menus, choices, and comments.
-        Takes care of propagating dependencies from enclosing menus and ifs."""
+                # We always strip whitespace after tokens, so it is safe to
+                # assume that s[i] is the start of a token here.
+                c = s[i]
 
-        def parse_val_and_cond(tokens, line, filename, linenr):
-            """Parses '<expr1> if <expr2>' constructs, where the 'if' part is
-            optional. Returns a tuple containing the parsed expressions, with
-            None as the second element if the 'if' part is missing."""
-            return (self._parse_expr(tokens, stmt, line, filename, linenr,
-                                     False),
-                    self._parse_expr(tokens, stmt, line, filename, linenr)
-                    if tokens.check(T_IF) else None)
+                if c in "\"'":
+                    if "$" not in s and "\\" not in s:
+                        # Fast path for lines without $ and \. Find the
+                        # matching quote.
+                        end_i = s.find(c, i + 1) + 1
+                        if not end_i:
+                            self._parse_error("unterminated string")
+                        val = s[i + 1:end_i - 1]
+                        i = end_i
+                    else:
+                        # Slow path
+                        s, end_i = self._expand_str(s, i)
 
-        # In case the symbol is defined in multiple locations, we need to
-        # remember what prompts, defaults, selects, and implies are new for
-        # this definition, as "depends on" should only apply to the local
-        # definition.
-        new_prompt = None
-        new_def_exprs = []
-        new_selects = []
-        new_implies = []
+                        # os.path.expandvars() and the $UNAME_RELEASE replace()
+                        # is a backwards compatibility hack, which should be
+                        # reasonably safe as expandvars() leaves references to
+                        # undefined env. vars. as is.
+                        #
+                        # The preprocessor functionality changed how
+                        # environment variables are referenced, to $(FOO).
+                        val = expandvars(s[i + 1:end_i - 1]
+                                         .replace("$UNAME_RELEASE",
+                                                  _UNAME_RELEASE))
 
-        # Dependencies from 'depends on' statements
-        depends_on_expr = None
+                        i = end_i
 
+                    # This is the only place where we don't survive with a
+                    # single token of lookback: 'option env="FOO"' does not
+                    # refer to a constant symbol named "FOO".
+                    token = \
+                        val if token in _STRING_LEX or tokens[0] is _T_OPTION \
+                        else self._lookup_const_sym(val)
+
+                elif s.startswith("&&", i):
+                    token = _T_AND
+                    i += 2
+
+                elif s.startswith("||", i):
+                    token = _T_OR
+                    i += 2
+
+                elif c == "=":
+                    token = _T_EQUAL
+                    i += 1
+
+                elif s.startswith("!=", i):
+                    token = _T_UNEQUAL
+                    i += 2
+
+                elif c == "!":
+                    token = _T_NOT
+                    i += 1
+
+                elif c == "(":
+                    token = _T_OPEN_PAREN
+                    i += 1
+
+                elif c == ")":
+                    token = _T_CLOSE_PAREN
+                    i += 1
+
+                elif c == "#":
+                    break
+
+
+                # Very rare
+
+                elif s.startswith("<=", i):
+                    token = _T_LESS_EQUAL
+                    i += 2
+
+                elif c == "<":
+                    token = _T_LESS
+                    i += 1
+
+                elif s.startswith(">=", i):
+                    token = _T_GREATER_EQUAL
+                    i += 2
+
+                elif c == ">":
+                    token = _T_GREATER
+                    i += 1
+
+
+                else:
+                    self._parse_error("unknown tokens in line")
+
+
+                # Skip trailing whitespace
+                while i < len(s) and s[i].isspace():
+                    i += 1
+
+
+            # Add the token
+            tokens.append(token)
+
+        # None-terminating the token list makes token fetching simpler/faster
+        tokens.append(None)
+
+        return tokens
+
+    # Helpers for syntax checking and token fetching. See the
+    # 'Intro to expressions' section for what a constant symbol is.
+    #
+    # More of these could be added, but the single-use cases are inlined as an
+    # optimization.
+
+    def _expect_sym(self):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
+
+        if token.__class__ is not Symbol:
+            self._parse_error("expected symbol")
+
+        return token
+
+    def _expect_nonconst_sym(self):
+        # Used for 'select' and 'imply' only. We know the token indices.
+
+        token = self._tokens[1]
+        self._tokens_i = 2
+
+        if token.__class__ is not Symbol or token.is_constant:
+            self._parse_error("expected nonconstant symbol")
+
+        return token
+
+    def _expect_str_and_eol(self):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
+
+        if token.__class__ is not str:
+            self._parse_error("expected string")
+
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
+
+        return token
+
+    def _expect_expr_and_eol(self):
+        expr = self._parse_expr(True)
+
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
+
+        return expr
+
+    def _check_token(self, token):
+        # If the next token is 'token', removes it and returns True
+
+        if self._tokens[self._tokens_i] is token:
+            self._tokens_i += 1
+            return True
+        return False
+
+    #
+    # Preprocessor logic
+    #
+
+    def _parse_assignment(self, s):
+        # Parses a preprocessor variable assignment, registering the variable
+        # if it doesn't already exist. Also takes care of bare macros on lines
+        # (which are allowed, and can be useful for their side effects).
+
+        # Expand any macros in the left-hand side of the assignment (the
+        # variable name)
+        s = s.lstrip()
+        i = 0
         while 1:
-            line = line_feeder.get_next()
-            if line is None:
+            i = _assignment_lhs_fragment_match(s, i).end()
+            if s.startswith("$(", i):
+                s, i = self._expand_macro(s, i, ())
+            else:
                 break
 
-            filename = line_feeder.filename
-            linenr = line_feeder.linenr
+        if s.isspace():
+            # We also accept a bare macro on a line (e.g.
+            # $(warning-if,$(foo),ops)), provided it expands to a blank string
+            return
 
-            tokens = self._tokenize(line, False, filename, linenr)
+        # Assigned variable
+        name = s[:i]
 
-            t0 = tokens.get_next()
-            if t0 is None:
+
+        # Extract assignment operator (=, :=, or +=) and value
+        rhs_match = _assignment_rhs_match(s, i)
+        if not rhs_match:
+            self._parse_error("syntax error")
+
+        op, val = rhs_match.groups()
+
+
+        if name in self.variables:
+            # Already seen variable
+            var = self.variables[name]
+        else:
+            # New variable
+            var = Variable()
+            var.kconfig = self
+            var.name = name
+            var._n_expansions = 0
+            self.variables[name] = var
+
+            # += acts like = on undefined variables (defines a recursive
+            # variable)
+            if op == "+=":
+                op = "="
+
+        if op == "=":
+            var.is_recursive = True
+            var.value = val
+        elif op == ":=":
+            var.is_recursive = False
+            var.value = self._expand_whole(val, ())
+        else:  # op == "+="
+            # += does immediate expansion if the variable was last set
+            # with :=
+            var.value += " " + (val if var.is_recursive else
+                                self._expand_whole(val, ()))
+
+    def _expand_whole(self, s, args):
+        # Expands preprocessor macros in all of 's'. Used whenever we don't
+        # have to worry about delimiters. See _expand_macro() re. the 'args'
+        # parameter.
+        #
+        # Returns the expanded string.
+
+        i = 0
+        while 1:
+            i = s.find("$(", i)
+            if i == -1:
+                break
+            s, i = self._expand_macro(s, i, args)
+        return s
+
+    def _expand_name(self, s, i):
+        # Expands a symbol name starting at index 'i' in 's'.
+        #
+        # Returns the expanded name, the expanded 's' (including the part
+        # before the name), and the index of the first character in the next
+        # token after the name.
+
+        s, end_i = self._expand_name_iter(s, i)
+        name = s[i:end_i]
+        # isspace() is False for empty strings
+        if not name.strip():
+            # Avoid creating a Kconfig symbol with a blank name. It's almost
+            # guaranteed to be an error.
+            self._parse_error("macro expanded to blank string")
+
+        # Skip trailing whitespace
+        while end_i < len(s) and s[end_i].isspace():
+            end_i += 1
+
+        return name, s, end_i
+
+    def _expand_name_iter(self, s, i):
+        # Expands a symbol name starting at index 'i' in 's'.
+        #
+        # Returns the expanded 's' (including the part before the name) and the
+        # index of the first character after the expanded name in 's'.
+
+        while 1:
+            match = _name_special_search(s, i)
+
+            if match.group() == "$(":
+                s, i = self._expand_macro(s, match.start(), ())
+            else:
+                return (s, match.start())
+
+    def _expand_str(self, s, i):
+        # Expands a quoted string starting at index 'i' in 's'. Handles both
+        # backslash escapes and macro expansion.
+        #
+        # Returns the expanded 's' (including the part before the string) and
+        # the index of the first character after the expanded string in 's'.
+
+        quote = s[i]
+        i += 1  # Skip over initial "/'
+        while 1:
+            match = _string_special_search(s, i)
+            if not match:
+                self._parse_error("unterminated string")
+
+
+            if match.group() == quote:
+                # Found the end of the string
+                return (s, match.end())
+
+            elif match.group() == "\\":
+                # Replace '\x' with 'x'. 'i' ends up pointing to the character
+                # after 'x', which allows macros to be canceled with '\$(foo)'.
+                i = match.end()
+                s = s[:match.start()] + s[i:]
+
+            elif match.group() == "$(":
+                # A macro call within the string
+                s, i = self._expand_macro(s, match.start(), ())
+
+            else:
+                # A ' quote within " quotes or vice versa
+                i += 1
+
+    def _expand_macro(self, s, i, args):
+        # Expands a macro starting at index 'i' in 's'. If this macro resulted
+        # from the expansion of another macro, 'args' holds the arguments
+        # passed to that macro.
+        #
+        # Returns the expanded 's' (including the part before the macro) and
+        # the index of the first character after the expanded macro in 's'.
+
+        start = i
+        i += 2  # Skip over "$("
+
+        # Start of current macro argument
+        arg_start = i
+
+        # Arguments of this macro call
+        new_args = []
+
+        while 1:
+            match = _macro_special_search(s, i)
+            if not match:
+                self._parse_error("missing end parenthesis in macro expansion")
+
+
+            if match.group() == ")":
+                # Found the end of the macro
+
+                new_args.append(s[arg_start:match.start()])
+
+                prefix = s[:start]
+
+                # $(1) is replaced by the first argument to the function, etc.,
+                # provided at least that many arguments were passed
+
+                try:
+                    # Does the macro look like an integer, with a corresponding
+                    # argument? If so, expand it to the value of the argument.
+                    prefix += args[int(new_args[0])]
+                except (ValueError, IndexError):
+                    # Regular variables are just functions without arguments,
+                    # and also go through the function value path
+                    prefix += self._fn_val(new_args)
+
+                return (prefix + s[match.end():],
+                        len(prefix))
+
+            elif match.group() == ",":
+                # Found the end of a macro argument
+                new_args.append(s[arg_start:match.start()])
+                arg_start = i = match.end()
+
+            else:  # match.group() == "$("
+                # A nested macro call within the macro
+                s, i = self._expand_macro(s, match.start(), args)
+
+    def _fn_val(self, args):
+        # Returns the result of calling the function args[0] with the arguments
+        # args[1..len(args)-1]. Plain variables are treated as functions
+        # without arguments.
+
+        fn = args[0]
+
+        if fn in self.variables:
+            var = self.variables[fn]
+
+            if len(args) == 1:
+                # Plain variable
+                if var._n_expansions:
+                    self._parse_error("Preprocessor variable {} recursively "
+                                      "references itself".format(var.name))
+            elif var._n_expansions > 100:
+                # Allow functions to call themselves, but guess that functions
+                # that are overly recursive are stuck
+                self._parse_error("Preprocessor function {} seems stuck "
+                                  "in infinite recursion".format(var.name))
+
+            var._n_expansions += 1
+            res = self._expand_whole(self.variables[fn].value, args)
+            var._n_expansions -= 1
+            return res
+
+        if fn in self._functions:
+            # Built-in or user-defined function
+
+            py_fn, min_arg, max_arg = self._functions[fn]
+
+            if len(args) - 1 < min_arg or \
+               (max_arg is not None and len(args) - 1 > max_arg):
+
+                if min_arg == max_arg:
+                    expected_args = min_arg
+                elif max_arg is None:
+                    expected_args = "{} or more".format(min_arg)
+                else:
+                    expected_args = "{}-{}".format(min_arg, max_arg)
+
+                raise KconfigError("{}:{}: bad number of arguments in call "
+                                   "to {}, expected {}, got {}"
+                                   .format(self.filename, self.linenr, fn,
+                                           expected_args, len(args) - 1))
+
+            return py_fn(self, *args)
+
+        # Environment variables are tried last
+        if fn in os.environ:
+            self.env_vars.add(fn)
+            return os.environ[fn]
+
+        return ""
+
+    #
+    # Parsing
+    #
+
+    def _make_and(self, e1, e2):
+        # Constructs an AND (&&) expression. Performs trivial simplification.
+
+        if e1 is self.y:
+            return e2
+
+        if e2 is self.y:
+            return e1
+
+        if e1 is self.n or e2 is self.n:
+            return self.n
+
+        return (AND, e1, e2)
+
+    def _make_or(self, e1, e2):
+        # Constructs an OR (||) expression. Performs trivial simplification.
+
+        if e1 is self.n:
+            return e2
+
+        if e2 is self.n:
+            return e1
+
+        if e1 is self.y or e2 is self.y:
+            return self.y
+
+        return (OR, e1, e2)
+
+    def _parse_block(self, end_token, parent, prev):
+        # Parses a block, which is the contents of either a file or an if,
+        # menu, or choice statement.
+        #
+        # end_token:
+        #   The token that ends the block, e.g. _T_ENDIF ("endif") for ifs.
+        #   None for files.
+        #
+        # parent:
+        #   The parent menu node, corresponding to a menu, Choice, or 'if'.
+        #   'if's are flattened after parsing.
+        #
+        # prev:
+        #   The previous menu node. New nodes will be added after this one (by
+        #   modifying their 'next' pointer).
+        #
+        #   'prev' is reused to parse a list of child menu nodes (for a menu or
+        #   Choice): After parsing the children, the 'next' pointer is assigned
+        #   to the 'list' pointer to "tilt up" the children above the node.
+        #
+        # Returns the final menu node in the block (or 'prev' if the block is
+        # empty). This allows chaining.
+
+        while self._next_line():
+            t0 = self._tokens[0]
+
+            if t0 is _T_CONFIG or t0 is _T_MENUCONFIG:
+                # The tokenizer allocates Symbol objects for us
+                sym = self._tokens[1]
+
+                if sym.__class__ is not Symbol or sym.is_constant:
+                    self._parse_error("missing or bad symbol name")
+
+                if self._tokens[2] is not None:
+                    self._trailing_tokens_error()
+
+                self.defined_syms.append(sym)
+
+                node = MenuNode()
+                node.kconfig = self
+                node.item = sym
+                node.is_menuconfig = (t0 is _T_MENUCONFIG)
+                node.prompt = node.help = node.list = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                sym.nodes.append(node)
+
+                self._parse_properties(node)
+
+                if node.is_menuconfig and not node.prompt:
+                    self._warn("the menuconfig symbol {} has no prompt"
+                               .format(_name_and_loc(sym)))
+
+                # Equivalent to
+                #
+                #   prev.next = node
+                #   prev = node
+                #
+                # due to tricky Python semantics. The order matters.
+                prev.next = prev = node
+
+            elif t0 is None:
+                # Blank line
                 continue
 
-            # Cases are ordered roughly by frequency, which speeds things up a
-            # bit
+            elif t0 in _SOURCE_TOKENS:
+                pattern = self._expect_str_and_eol()
 
-            if t0 == T_DEPENDS:
-                if not tokens.check(T_ON):
-                    _parse_error(line, 'expected "on" after "depends"',
-                                 filename, linenr)
+                if t0 in _REL_SOURCE_TOKENS:
+                    # Relative source
+                    pattern = join(dirname(self.filename), pattern)
 
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
-                                               linenr)
+                # - glob() doesn't support globbing relative to a directory, so
+                #   we need to prepend $srctree to 'pattern'. Use join()
+                #   instead of '+' so that an absolute path in 'pattern' is
+                #   preserved.
+                #
+                # - Sort the glob results to ensure a consistent ordering of
+                #   Kconfig symbols, which indirectly ensures a consistent
+                #   ordering in e.g. .config files
+                filenames = sorted(iglob(join(self._srctree_prefix, pattern)))
 
-                if isinstance(stmt, (Menu, Comment)):
-                    stmt.orig_deps = _make_and(stmt.orig_deps, parsed_deps)
+                if not filenames and t0 in _OBL_SOURCE_TOKENS:
+                    raise KconfigError(
+                        "{}:{}: '{}' not found (in '{}'). Check that "
+                        "environment variables are set correctly (e.g. "
+                        "$srctree, which is {}). Also note that unset "
+                        "environment variables expand to the empty string."
+                        .format(self.filename, self.linenr, pattern,
+                                self._line.strip(),
+                                "set to '{}'".format(self.srctree)
+                                    if self.srctree else "unset or blank"))
+
+                for filename in filenames:
+                    self._enter_file(filename)
+                    prev = self._parse_block(None, parent, prev)
+                    self._leave_file()
+
+            elif t0 is end_token:
+                # Reached the end of the block. Terminate the final node and
+                # return it.
+
+                if self._tokens[1] is not None:
+                    self._trailing_tokens_error()
+
+                prev.next = None
+                return prev
+
+            elif t0 is _T_IF:
+                node = MenuNode()
+                node.item = node.prompt = None
+                node.parent = parent
+                node.dep = self._expect_expr_and_eol()
+
+                self._parse_block(_T_ENDIF, node, node)
+                node.list = node.next
+
+                prev.next = prev = node
+
+            elif t0 is _T_MENU:
+                node = MenuNode()
+                node.kconfig = self
+                node.item = t0  # _T_MENU == MENU
+                node.is_menuconfig = True
+                node.prompt = (self._expect_str_and_eol(), self.y)
+                node.visibility = self.y
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                self.menus.append(node)
+
+                self._parse_properties(node)
+                self._parse_block(_T_ENDMENU, node, node)
+                node.list = node.next
+
+                prev.next = prev = node
+
+            elif t0 is _T_COMMENT:
+                node = MenuNode()
+                node.kconfig = self
+                node.item = t0  # _T_COMMENT == COMMENT
+                node.is_menuconfig = False
+                node.prompt = (self._expect_str_and_eol(), self.y)
+                node.list = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                self.comments.append(node)
+
+                self._parse_properties(node)
+
+                prev.next = prev = node
+
+            elif t0 is _T_CHOICE:
+                if self._tokens[1] is None:
+                    choice = Choice()
+                    choice.direct_dep = self.n
                 else:
-                    depends_on_expr = _make_and(depends_on_expr, parsed_deps)
+                    # Named choice
+                    name = self._expect_str_and_eol()
+                    choice = self.named_choices.get(name)
+                    if not choice:
+                        choice = Choice()
+                        choice.name = name
+                        choice.direct_dep = self.n
+                        self.named_choices[name] = choice
 
-            elif t0 == T_HELP:
-                # Find first non-blank (not all-space) line and get its
-                # indentation
-                line = line_feeder.next_nonblank()
-                if line is None:
-                    stmt.help = ""
-                    break
-                indent = _indentation(line)
-                if indent == 0:
-                    # If the first non-empty lines has zero indent, there is no
-                    # help text
-                    stmt.help = ""
-                    line_feeder.unget()
-                    break
+                self.choices.append(choice)
 
-                # The help text goes on till the first non-empty line with less
-                # indent
-                help_lines = [_deindent(line, indent)]
-                while 1:
-                    line = line_feeder.get_next()
-                    if line is None or \
-                       (not line.isspace() and _indentation(line) < indent):
-                        stmt.help = "".join(help_lines)
-                        break
-                    help_lines.append(_deindent(line, indent))
+                node = MenuNode()
+                node.kconfig = choice.kconfig = self
+                node.item = choice
+                node.is_menuconfig = True
+                node.prompt = node.help = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
 
-                if line is None:
-                    break
+                choice.nodes.append(node)
 
-                line_feeder.unget()
+                self._parse_properties(node)
+                self._parse_block(_T_ENDCHOICE, node, node)
+                node.list = node.next
 
-            elif t0 == T_SELECT:
-                target = tokens.get_next()
+                prev.next = prev = node
 
-                stmt.referenced_syms.add(target)
-                stmt.selected_syms.add(target)
+            elif t0 is _T_MAINMENU:
+                self.top_node.prompt = (self._expect_str_and_eol(), self.y)
 
-                new_selects.append(
-                    (target,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+            else:
+                # A valid endchoice/endif/endmenu is caught by the 'end_token'
+                # check above
+                self._parse_error(
+                    "no corresponding 'choice'" if t0 is _T_ENDCHOICE else
+                    "no corresponding 'if'"     if t0 is _T_ENDIF else
+                    "no corresponding 'menu'"   if t0 is _T_ENDMENU else
+                    "unrecognized construct")
 
-            elif t0 == T_IMPLY:
-                target = tokens.get_next()
+        # End of file reached. Terminate the final node and return it.
 
-                stmt.referenced_syms.add(target)
-                stmt.implied_syms.add(target)
+        if end_token:
+            raise KconfigError(
+                "expected '{}' at end of '{}'"
+                .format("endchoice" if end_token is _T_ENDCHOICE else
+                        "endif"     if end_token is _T_ENDIF else
+                        "endmenu",
+                        self.filename))
 
-                new_implies.append(
-                    (target,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+        prev.next = None
+        return prev
 
-            elif t0 in (T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING):
-                stmt.type = TOKEN_TO_TYPE[t0]
-                if tokens.peek_next() is not None:
-                    new_prompt = parse_val_and_cond(tokens, line, filename,
-                                                    linenr)
+    def _parse_cond(self):
+        # Parses an optional 'if <expr>' construct and returns the parsed
+        # <expr>, or self.y if the next token is not _T_IF
 
-            elif t0 == T_DEFAULT:
-                new_def_exprs.append(parse_val_and_cond(tokens, line, filename,
-                                                        linenr))
+        expr = self._parse_expr(True) if self._check_token(_T_IF) else self.y
 
-            elif t0 == T_DEF_BOOL:
-                stmt.type = BOOL
-                if tokens.peek_next() is not None:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line,
-                                                            filename, linenr))
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
 
-            elif t0 == T_PROMPT:
-                # 'prompt' properties override each other within a single
-                # definition of a symbol, but additional prompts can be added
-                # by defining the symbol multiple times; hence 'new_prompt'
-                # instead of 'prompt'.
-                new_prompt = parse_val_and_cond(tokens, line, filename, linenr)
+        return expr
 
-            elif t0 == T_RANGE:
-                low = tokens.get_next()
-                high = tokens.get_next()
-                stmt.referenced_syms.add(low)
-                stmt.referenced_syms.add(high)
+    def _parse_properties(self, node):
+        # Parses and adds properties to the MenuNode 'node' (type, 'prompt',
+        # 'default's, etc.) Properties are later copied up to symbols and
+        # choices in a separate pass after parsing, in e.g.
+        # _add_props_to_sym().
+        #
+        # An older version of this code added properties directly to symbols
+        # and choices instead of to their menu nodes (and handled dependency
+        # propagation simultaneously), but that loses information on where a
+        # property is added when a symbol or choice is defined in multiple
+        # locations. Some Kconfig configuration systems rely heavily on such
+        # symbols, and better docs can be generated by keeping track of where
+        # properties are added.
+        #
+        # node:
+        #   The menu node we're parsing properties on
 
-                stmt.ranges.append(
-                    (low, high,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+        # Dependencies from 'depends on'. Will get propagated to the properties
+        # below.
+        node.dep = self.y
 
-            elif t0 == T_DEF_TRISTATE:
-                stmt.type = TRISTATE
-                if tokens.peek_next() is not None:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line,
-                                                            filename, linenr))
+        while self._next_line():
+            t0 = self._tokens[0]
 
-            elif t0 == T_OPTION:
-                if tokens.check(T_ENV) and tokens.check(T_EQUAL):
-                    env_var = tokens.get_next()
+            if t0 in _TYPE_TOKENS:
+                # Relies on '_T_BOOL is BOOL', etc., to save a conversion
+                self._set_type(node, t0)
+                if self._tokens[1] is not None:
+                    self._parse_prompt(node)
 
-                    stmt.is_special_ = True
-                    stmt.is_from_env = True
+            elif t0 is _T_DEPENDS:
+                if not self._check_token(_T_ON):
+                    self._parse_error("expected 'on' after 'depends'")
 
-                    if env_var not in os.environ:
-                        self._warn("The symbol {0} references the "
-                                   "non-existent environment variable {1} and "
-                                   "will get the empty string as its value. "
-                                   "If you're using Kconfiglib via "
-                                   "'make (i)scriptconfig', it should have "
-                                   "set up the environment correctly for you. "
-                                   "If you still got this message, that "
-                                   "might be an error, and you should email "
-                                   "ulfalizer a.t Google's email service."""
-                                   .format(stmt.name, env_var),
-                                   filename, linenr)
+                node.dep = self._make_and(node.dep,
+                                          self._expect_expr_and_eol())
 
-                        stmt.cached_val = ""
+            elif t0 is _T_HELP:
+                self._parse_help(node)
+
+            elif t0 is _T_SELECT:
+                if node.item.__class__ is not Symbol:
+                    self._parse_error("only symbols can select")
+
+                node.selects.append((self._expect_nonconst_sym(),
+                                     self._parse_cond()))
+
+            elif t0 is None:
+                # Blank line
+                continue
+
+            elif t0 is _T_DEFAULT:
+                node.defaults.append((self._parse_expr(False),
+                                      self._parse_cond()))
+
+            elif t0 in _DEF_TOKEN_TO_TYPE:
+                self._set_type(node, _DEF_TOKEN_TO_TYPE[t0])
+                node.defaults.append((self._parse_expr(False),
+                                      self._parse_cond()))
+
+            elif t0 is _T_PROMPT:
+                self._parse_prompt(node)
+
+            elif t0 is _T_RANGE:
+                node.ranges.append((self._expect_sym(), self._expect_sym(),
+                                    self._parse_cond()))
+
+            elif t0 is _T_IMPLY:
+                if node.item.__class__ is not Symbol:
+                    self._parse_error("only symbols can imply")
+
+                node.implies.append((self._expect_nonconst_sym(),
+                                     self._parse_cond()))
+
+            elif t0 is _T_VISIBLE:
+                if not self._check_token(_T_IF):
+                    self._parse_error("expected 'if' after 'visible'")
+
+                node.visibility = self._make_and(node.visibility,
+                                                 self._expect_expr_and_eol())
+
+            elif t0 is _T_OPTION:
+                if self._check_token(_T_ENV):
+                    if not self._check_token(_T_EQUAL):
+                        self._parse_error("expected '=' after 'env'")
+
+                    env_var = self._expect_str_and_eol()
+                    node.item.env_var = env_var
+
+                    if env_var in os.environ:
+                        node.defaults.append(
+                            (self._lookup_const_sym(os.environ[env_var]),
+                             self.y))
                     else:
-                        stmt.cached_val = os.environ[env_var]
+                        self._warn("{1} has 'option env=\"{0}\"', "
+                                   "but the environment variable {0} is not "
+                                   "set".format(node.item.name, env_var),
+                                   self.filename, self.linenr)
 
-                elif tokens.check(T_DEFCONFIG_LIST):
-                    self.defconfig_sym = stmt
+                    if env_var != node.item.name:
+                        self._warn("Kconfiglib expands environment variables "
+                                   "in strings directly, meaning you do not "
+                                   "need 'option env=...' \"bounce\" symbols. "
+                                   "For compatibility with the C tools, "
+                                   "rename {} to {} (so that the symbol name "
+                                   "matches the environment variable name)."
+                                   .format(node.item.name, env_var),
+                                   self.filename, self.linenr)
 
-                elif tokens.check(T_MODULES):
+                elif self._check_token(_T_DEFCONFIG_LIST):
+                    if not self.defconfig_list:
+                        self.defconfig_list = node.item
+                    else:
+                        self._warn("'option defconfig_list' set on multiple "
+                                   "symbols ({0} and {1}). Only {0} will be "
+                                   "used.".format(self.defconfig_list.name,
+                                                  node.item.name),
+                                   self.filename, self.linenr)
+
+                elif self._check_token(_T_MODULES):
                     # To reduce warning spam, only warn if 'option modules' is
                     # set on some symbol that isn't MODULES, which should be
                     # safe. I haven't run into any projects that make use
                     # modules besides the kernel yet, and there it's likely to
                     # keep being called "MODULES".
-                    if stmt.name != "MODULES":
+                    if node.item is not self.modules:
                         self._warn("the 'modules' option is not supported. "
-                                   "Let me know if this is a problem for you; "
-                                   "it shouldn't be that hard to implement. "
-                                   "(Note that modules are still supported -- "
+                                   "Let me know if this is a problem for you, "
+                                   "as it wouldn't be that hard to implement. "
+                                   "Note that modules are supported -- "
                                    "Kconfiglib just assumes the symbol name "
                                    "MODULES, like older versions of the C "
                                    "implementation did when 'option modules' "
-                                   "wasn't used.)",
-                                   filename, linenr)
+                                   "wasn't used.",
+                                   self.filename, self.linenr)
 
-                elif tokens.check(T_ALLNOCONFIG_Y):
-                    if not isinstance(stmt, Symbol):
-                        _parse_error(line,
-                                     "the 'allnoconfig_y' option is only "
-                                     "valid for symbols",
-                                     filename, linenr)
-                    stmt.allnoconfig_y = True
+                elif self._check_token(_T_ALLNOCONFIG_Y):
+                    if node.item.__class__ is not Symbol:
+                        self._parse_error("the 'allnoconfig_y' option is only "
+                                          "valid for symbols")
+
+                    node.item.is_allnoconfig_y = True
 
                 else:
-                    _parse_error(line, "unrecognized option", filename, linenr)
+                    self._parse_error("unrecognized option")
 
-            elif t0 == T_VISIBLE:
-                if not tokens.check(T_IF):
-                    _parse_error(line, 'expected "if" after "visible"',
-                                 filename, linenr)
-                if not isinstance(stmt, Menu):
-                    _parse_error(line,
-                                 "'visible if' is only valid for menus",
-                                 filename, linenr)
+            elif t0 is _T_OPTIONAL:
+                if node.item.__class__ is not Choice:
+                    self._parse_error('"optional" is only valid for choices')
 
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
-                                               linenr)
-                stmt.visible_if_expr = _make_and(stmt.visible_if_expr,
-                                                 parsed_deps)
-
-            elif t0 == T_OPTIONAL:
-                if not isinstance(stmt, Choice):
-                    _parse_error(line,
-                                 '"optional" is only valid for choices',
-                                 filename,
-                                 linenr)
-                stmt.optional = True
+                node.item.is_optional = True
 
             else:
-                # See comment in Config.__init__()
-                self.end_line = line
-                self.end_line_tokens = tokens
+                # Reuse the tokens for the non-property line later
+                self._reuse_tokens = True
+                return
+
+    def _set_type(self, node, new_type):
+        # UNKNOWN is falsy
+        if node.item.orig_type and node.item.orig_type is not new_type:
+            self._warn("{} defined with multiple types, {} will be used"
+                       .format(_name_and_loc(node.item),
+                               TYPE_TO_STR[new_type]))
+
+        node.item.orig_type = new_type
+
+    def _parse_prompt(self, node):
+        # 'prompt' properties override each other within a single definition of
+        # a symbol, but additional prompts can be added by defining the symbol
+        # multiple times
+
+        if node.prompt:
+            self._warn(_name_and_loc(node.item) +
+                       " defined with multiple prompts in single location")
+
+        prompt = self._tokens[1]
+        self._tokens_i = 2
+
+        if prompt.__class__ is not str:
+            self._parse_error("expected prompt string")
+
+        if prompt != prompt.strip():
+            self._warn(_name_and_loc(node.item) +
+                       " has leading or trailing whitespace in its prompt")
+
+            # This avoid issues for e.g. reStructuredText documentation, where
+            # '*prompt *' is invalid
+            prompt = prompt.strip()
+
+        node.prompt = (prompt, self._parse_cond())
+
+    def _parse_help(self, node):
+        if node.help is not None:
+            self._warn(_name_and_loc(node.item) + " defined with more than "
+                       "one help text -- only the last one will be used")
+
+        # Micro-optimization. This code is pretty hot.
+        readline = self._readline
+
+        # Find first non-blank (not all-space) line and get its
+        # indentation
+
+        while 1:
+            line = readline()
+            self.linenr += 1
+            if not line:
+                self._empty_help(node, line)
+                return
+            if not line.isspace():
                 break
 
-        # Done parsing properties. Now propagate 'depends on' and enclosing
-        # menu/if dependencies to expressions.
+        len_ = len  # Micro-optimization
 
-        # The set of symbols referenced directly by the statement plus all
-        # symbols referenced by enclosing menus and ifs
-        stmt.all_referenced_syms = stmt.referenced_syms | _get_expr_syms(deps)
+        # Use a separate 'expline' variable here and below to avoid stomping on
+        # any tabs people might've put deliberately into the first line after
+        # the help text
+        expline = line.expandtabs()
+        indent = len_(expline) - len_(expline.lstrip())
+        if not indent:
+            self._empty_help(node, line)
+            return
 
-        # Save original dependencies from enclosing menus and ifs
-        stmt.deps_from_containing = deps
+        # The help text goes on till the first non-blank line with less indent
+        # than the first line
 
-        if isinstance(stmt, (Menu, Comment)):
-            stmt.dep_expr = _make_and(stmt.orig_deps, deps)
-        else:
-            # Symbol or Choice
+        # Add the first line
+        lines = [expline[indent:]]
+        add_line = lines.append  # Micro-optimization
 
-            # See comment for 'menu_dep'
-            stmt.menu_dep = _make_and(deps, depends_on_expr)
+        while 1:
+            line = readline()
+            if line.isspace():
+                # No need to preserve the exact whitespace in these
+                add_line("\n")
+            elif not line:
+                # End of file
+                break
+            else:
+                expline = line.expandtabs()
+                if len_(expline) - len_(expline.lstrip()) < indent:
+                    break
+                add_line(expline[indent:])
 
-            # Propagate dependencies to prompts
+        self.linenr += len_(lines)
+        node.help = "".join(lines).rstrip()
+        if line:
+            self._line_after_help(line)
 
-            if new_prompt is not None:
-                prompt, cond_expr = new_prompt
-                # Propagate 'visible if' dependencies from menus and local
-                # 'depends on' dependencies
-                cond_expr = _make_and(_make_and(cond_expr, visible_if_deps),
-                                      depends_on_expr)
-                # Save original
-                stmt.orig_prompts.append((prompt, cond_expr))
-                # Finalize with dependencies from enclosing menus and ifs
-                stmt.prompts.append((prompt, _make_and(cond_expr, deps)))
+    def _empty_help(self, node, line):
+        self._warn(_name_and_loc(node.item) +
+                   " has 'help' but empty help text")
+        node.help = ""
+        if line:
+            self._line_after_help(line)
 
-            # Propagate dependencies to defaults
+    def _parse_expr(self, transform_m):
+        # Parses an expression from the tokens in Kconfig._tokens using a
+        # simple top-down approach. See the module docstring for the expression
+        # format.
+        #
+        # transform_m:
+        #   True if m should be rewritten to m && MODULES. See the
+        #   Kconfig.eval_string() documentation.
 
-            # Propagate 'depends on' dependencies
-            new_def_exprs = [(val_expr, _make_and(cond_expr, depends_on_expr))
-                             for val_expr, cond_expr in new_def_exprs]
-            # Save original
-            stmt.orig_def_exprs.extend(new_def_exprs)
-            # Finalize with dependencies from enclosing menus and ifs
-            stmt.def_exprs.extend([(val_expr, _make_and(cond_expr, deps))
-                                   for val_expr, cond_expr in new_def_exprs])
+        # Grammar:
+        #
+        #   expr:     and_expr ['||' expr]
+        #   and_expr: factor ['&&' and_expr]
+        #   factor:   <symbol> ['='/'!='/'<'/... <symbol>]
+        #             '!' factor
+        #             '(' expr ')'
+        #
+        # It helps to think of the 'expr: and_expr' case as a single-operand OR
+        # (no ||), and of the 'and_expr: factor' case as a single-operand AND
+        # (no &&). Parsing code is always a bit tricky.
 
-            # Propagate dependencies to selects and implies
+        # Mind dump: parse_factor() and two nested loops for OR and AND would
+        # work as well. The straightforward implementation there gives a
+        # (op, (op, (op, A, B), C), D) parse for A op B op C op D. Representing
+        # expressions as (op, [list of operands]) instead goes nicely with that
+        # version, but is wasteful for short expressions and complicates
+        # expression evaluation and other code that works on expressions (more
+        # complicated code likely offsets any performance gain from less
+        # recursion too). If we also try to optimize the list representation by
+        # merging lists when possible (e.g. when ANDing two AND expressions),
+        # we end up allocating a ton of lists instead of reusing expressions,
+        # which is bad.
 
-            # Only symbols can select and imply
-            if isinstance(stmt, Symbol):
-                # Propagate 'depends on' dependencies
-                new_selects = [(target, _make_and(cond_expr, depends_on_expr))
-                               for target, cond_expr in new_selects]
-                new_implies = [(target, _make_and(cond_expr, depends_on_expr))
-                               for target, cond_expr in new_implies]
-                # Save original
-                stmt.orig_selects.extend(new_selects)
-                stmt.orig_implies.extend(new_implies)
-                # Finalize with dependencies from enclosing menus and ifs
-                for target, cond in new_selects:
-                    target.rev_dep = \
-                        _make_or(target.rev_dep,
-                                 _make_and(stmt, _make_and(cond, deps)))
-                for target, cond in new_implies:
-                    target.weak_rev_dep = \
-                        _make_or(target.weak_rev_dep,
-                                 _make_and(stmt, _make_and(cond, deps)))
+        and_expr = self._parse_and_expr(transform_m)
 
-    def _parse_expr(self, feed, cur_item, line, filename=None, linenr=None,
-                    transform_m=True):
-        """Parses an expression from the tokens in 'feed' using a simple
-        top-down approach. The result has the form
-        '(<operator>, [<parsed operands>])', where <operator> is e.g.
-        kconfiglib.AND. If there is only one operand (i.e., no && or ||), then
-        the operand is returned directly. This also goes for subexpressions.
+        # Return 'and_expr' directly if we have a "single-operand" OR.
+        # Otherwise, parse the expression on the right and make an OR node.
+        # This turns A || B || C || D into (OR, A, (OR, B, (OR, C, D))).
+        return and_expr if not self._check_token(_T_OR) else \
+            (OR, and_expr, self._parse_expr(transform_m))
 
-        feed: _Feed instance containing the tokens for the expression.
+    def _parse_and_expr(self, transform_m):
+        factor = self._parse_factor(transform_m)
 
-        cur_item: The item (Symbol, Choice, Menu, or Comment) currently being
-           parsed, or None if we're not parsing an item. Used for recording
-           references to symbols.
+        # Return 'factor' directly if we have a "single-operand" AND.
+        # Otherwise, parse the right operand and make an AND node. This turns
+        # A && B && C && D into (AND, A, (AND, B, (AND, C, D))).
+        return factor if not self._check_token(_T_AND) else \
+            (AND, factor, self._parse_and_expr(transform_m))
 
-        line: The line containing the expression being parsed.
+    def _parse_factor(self, transform_m):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
 
-        filename (default: None): The file containing the expression.
+        if token.__class__ is Symbol:
+            # Plain symbol or relation
 
-        linenr (default: None): The line number containing the expression.
+            if self._tokens[self._tokens_i] not in _RELATIONS:
+                # Plain symbol
 
-        transform_m (default: False): Determines if 'm' should be rewritten to
-           'm && MODULES' -- see parse_val_and_cond().
+                # For conditional expressions ('depends on <expr>',
+                # '... if <expr>', etc.), m is rewritten to m && MODULES.
+                if transform_m and token is self.m:
+                    return (AND, self.m, self.modules)
 
-        Expression grammar, in decreasing order of precedence:
-
-        <expr> -> <symbol>
-                  <symbol> '=' <symbol>
-                  <symbol> '!=' <symbol>
-                  '(' <expr> ')'
-                  '!' <expr>
-                  <expr> '&&' <expr>
-                  <expr> '||' <expr>"""
-
-        # Use instance variables to avoid having to pass these as arguments
-        # through the top-down parser in _parse_expr_rec(), which is tedious
-        # and obfuscates the code. A profiler run shows no noticeable
-        # performance difference.
-        self._cur_item = cur_item
-        self._transform_m = transform_m
-        self._line = line
-        self._filename = filename
-        self._linenr = linenr
-
-        return self._parse_expr_rec(feed)
-
-    def _parse_expr_rec(self, feed):
-        or_term = self._parse_or_term(feed)
-        if not feed.check(T_OR):
-            # Common case -- no need for an OR node since it's just a single
-            # operand
-            return or_term
-        or_terms = [or_term, self._parse_or_term(feed)]
-        while feed.check(T_OR):
-            or_terms.append(self._parse_or_term(feed))
-        return (OR, or_terms)
-
-    def _parse_or_term(self, feed):
-        and_term = self._parse_factor(feed)
-        if not feed.check(T_AND):
-            # Common case -- no need for an AND node since it's just a single
-            # operand
-            return and_term
-        and_terms = [and_term, self._parse_factor(feed)]
-        while feed.check(T_AND):
-            and_terms.append(self._parse_factor(feed))
-        return (AND, and_terms)
-
-    def _parse_factor(self, feed):
-        token = feed.get_next()
-
-        if isinstance(token, (Symbol, str)):
-            if self._cur_item is not None and isinstance(token, Symbol):
-                self._cur_item.referenced_syms.add(token)
-
-            next_token = feed.peek_next()
-            # For conditional expressions ('depends on <expr>',
-            # '... if <expr>', # etc.), "m" and m are rewritten to
-            # "m" && MODULES.
-            if next_token != T_EQUAL and next_token != T_UNEQUAL:
-                if self._transform_m and (token is self.m or token == "m"):
-                    return (AND, ["m", self._sym_lookup("MODULES")])
                 return token
 
-            relation = EQUAL if (feed.get_next() == T_EQUAL) else UNEQUAL
-            token_2 = feed.get_next()
-            if self._cur_item is not None and isinstance(token_2, Symbol):
-                self._cur_item.referenced_syms.add(token_2)
-            return (relation, token, token_2)
-
-        if token == T_NOT:
-            return (NOT, self._parse_factor(feed))
-
-        if token == T_OPEN_PAREN:
-            expr_parse = self._parse_expr_rec(feed)
-            if not feed.check(T_CLOSE_PAREN):
-                _parse_error(self._line, "missing end parenthesis",
-                             self._filename, self._linenr)
-            return expr_parse
-
-        _parse_error(self._line, "malformed expression", self._filename,
-                     self._linenr)
-
-    def _tokenize(self, s, for_eval, filename=None, linenr=None):
-        """Returns a _Feed instance containing tokens derived from the string
-        's'. Registers any new symbols encountered (via _sym_lookup()).
-
-        (I experimented with a pure regular expression implementation, but it
-        came out slower, less readable, and wouldn't have been as flexible.)
-
-        for_eval: True when parsing an expression for a call to Config.eval(),
-           in which case we should not treat the first token specially nor
-           register new symbols."""
-
-        s = s.strip()
-        if s == "" or s[0] == "#":
-            return _Feed([])
-
-        if for_eval:
-            previous = None # The previous token seen
-            tokens = []
-            i = 0 # The current index in the string being tokenized
-
-        else:
-            # The initial word on a line is parsed specially. Let
-            # command_chars = [A-Za-z0-9_]. Then
-            #  - leading non-command_chars characters are ignored, and
-            #  - the first token consists the following one or more
-            #    command_chars characters.
-            # This is why things like "----help--" are accepted.
-            initial_token_match = _initial_token_re_match(s)
-            if initial_token_match is None:
-                return _Feed([])
-            keyword = _get_keyword(initial_token_match.group(1))
-            if keyword == T_HELP:
-                # Avoid junk after "help", e.g. "---", being registered as a
-                # symbol
-                return _Feed([T_HELP])
-            if keyword is None:
-                # We expect a keyword as the first token
-                _tokenization_error(s, filename, linenr)
-
-            previous = keyword
-            tokens = [keyword]
-            # The current index in the string being tokenized
-            i = initial_token_match.end()
-
-        # _tokenize() is a hotspot during parsing, and this speeds things up a
-        # bit
-        strlen = len(s)
-        append = tokens.append
-
-        # Main tokenization loop. (Handles tokens past the first one.)
-        while i < strlen:
-            # Test for an identifier/keyword preceded by whitespace first; this
-            # is the most common case.
-            id_keyword_match = _id_keyword_re_match(s, i)
-            if id_keyword_match:
-                # We have an identifier or keyword. The above also stripped any
-                # whitespace for us.
-                name = id_keyword_match.group(1)
-                # Jump past it
-                i = id_keyword_match.end()
-
-                keyword = _get_keyword(name)
-                if keyword is not None:
-                    # It's a keyword
-                    append(keyword)
-                elif previous in STRING_LEX:
-                    # What would ordinarily be considered an identifier is
-                    # treated as a string after certain tokens
-                    append(name)
-                else:
-                    # It's a symbol name. _sym_lookup() will take care of
-                    # allocating a new Symbol instance if it's the first time
-                    # we see it.
-                    sym = self._sym_lookup(name, for_eval)
-
-                    if previous == T_CONFIG or previous == T_MENUCONFIG:
-                        # If the previous token is T_(MENU)CONFIG
-                        # ("(menu)config"), we're tokenizing the first line of
-                        # a symbol definition, and should remember this as a
-                        # location where the symbol is defined
-                        sym.def_locations.append((filename, linenr))
-                    else:
-                        # Otherwise, it's a reference to the symbol
-                        sym.ref_locations.append((filename, linenr))
-
-                    append(sym)
-
-            else:
-                # Not an identifier/keyword
-
-                while i < strlen and s[i].isspace():
-                    i += 1
-                if i == strlen:
-                    break
-                c = s[i]
-                i += 1
-
-                # String literal (constant symbol)
-                if c == '"' or c == "'":
-                    if "\\" in s:
-                        # Slow path: This could probably be sped up, but it's a
-                        # very unusual case anyway.
-                        quote = c
-                        val = ""
-                        while 1:
-                            if i >= len(s):
-                                _tokenization_error(s, filename, linenr)
-                            c = s[i]
-                            if c == quote:
-                                break
-                            if c == "\\":
-                                if i + 1 >= len(s):
-                                    _tokenization_error(s, filename, linenr)
-                                val += s[i + 1]
-                                i += 2
-                            else:
-                                val += c
-                                i += 1
-                        i += 1
-                        append(val)
-                    else:
-                        # Fast path: If the string contains no backslashes
-                        # (almost always) we can simply look for the matching
-                        # quote.
-                        end = s.find(c, i)
-                        if end == -1:
-                            _tokenization_error(s, filename, linenr)
-                        append(s[i:end])
-                        i = end + 1
-
-                elif c == "&":
-                    # Invalid characters are ignored
-                    if i >= len(s) or s[i] != "&": continue
-                    append(T_AND)
-                    i += 1
-
-                elif c == "|":
-                    # Invalid characters are ignored
-                    if i >= len(s) or s[i] != "|": continue
-                    append(T_OR)
-                    i += 1
-
-                elif c == "!":
-                    if i < len(s) and s[i] == "=":
-                        append(T_UNEQUAL)
-                        i += 1
-                    else:
-                        append(T_NOT)
-
-                elif c == "=": append(T_EQUAL)
-                elif c == "(": append(T_OPEN_PAREN)
-                elif c == ")": append(T_CLOSE_PAREN)
-                elif c == "#": break # Comment
-
-                else: continue # Invalid characters are ignored
-
-            previous = tokens[-1]
-
-        return _Feed(tokens)
-
-    def _sym_lookup(self, name, for_eval=False):
-        """Fetches the symbol 'name' from the symbol table, creating and
-        registering it if it does not exist. If 'for_eval' is True, the symbol
-        won't be added to the symbol table if it does not exist -- this is for
-        Config.eval()."""
-        if name in self.syms:
-            return self.syms[name]
-
-        new_sym = Symbol()
-        new_sym.config = self
-        new_sym.name = name
-        if for_eval:
-            self._warn("no symbol {0} in configuration".format(name))
-        else:
-            self.syms[name] = new_sym
-        return new_sym
-
-    #
-    # Expression evaluation
-    #
-
-    def _eval_expr(self, expr):
-        """Evaluates an expression to "n", "m", or "y"."""
-
-        # Handles e.g. an "x if y" condition where the "if y" part is missing.
-        if expr is None:
-            return "y"
-
-        res = self._eval_expr_rec(expr)
-        if res == "m":
-            # Promote "m" to "y" if we're running without modules.
+            # Relation
             #
-            # Internally, "m" is often rewritten to "m" && MODULES by both the
-            # C implementation and Kconfiglib, which takes care of cases where
-            # "m" should be demoted to "n" instead.
-            modules_sym = self.syms.get("MODULES")
-            if modules_sym is None or modules_sym.get_value() != "y":
-                return "y"
-        return res
+            # _T_EQUAL, _T_UNEQUAL, etc., deliberately have the same values as
+            # EQUAL, UNEQUAL, etc., so we can just use the token directly
+            self._tokens_i += 1
+            return (self._tokens[self._tokens_i - 1], token,
+                    self._expect_sym())
 
-    def _eval_expr_rec(self, expr):
-        if isinstance(expr, Symbol):
-            # Non-bool/tristate symbols are always "n" in a tristate sense,
-            # regardless of their value
-            if expr.type != BOOL and expr.type != TRISTATE:
-                return "n"
-            return expr.get_value()
+        if token is _T_NOT:
+            # token == _T_NOT == NOT
+            return (token, self._parse_factor(transform_m))
 
-        if isinstance(expr, str):
-            return expr if (expr == "y" or expr == "m") else "n"
+        if token is _T_OPEN_PAREN:
+            expr_parse = self._parse_expr(transform_m)
+            if self._check_token(_T_CLOSE_PAREN):
+                return expr_parse
 
-        # Ordered by frequency
-
-        if expr[0] == AND:
-            res = "y"
-            for subexpr in expr[1]:
-                ev = self._eval_expr_rec(subexpr)
-                # Return immediately upon discovering an "n" term
-                if ev == "n":
-                    return "n"
-                if ev == "m":
-                    res = "m"
-            # 'res' is either "m" or "y" here; we already handled the
-            # short-circuiting "n" case in the loop.
-            return res
-
-        if expr[0] == NOT:
-            ev = self._eval_expr_rec(expr[1])
-            if ev == "y":
-                return "n"
-            return "y" if (ev == "n") else "m"
-
-        if expr[0] == OR:
-            res = "n"
-            for subexpr in expr[1]:
-                ev = self._eval_expr_rec(subexpr)
-                # Return immediately upon discovering a "y" term
-                if ev == "y":
-                    return "y"
-                if ev == "m":
-                    res = "m"
-            # 'res' is either "n" or "m" here; we already handled the
-            # short-circuiting "y" case in the loop.
-            return res
-
-        if expr[0] == EQUAL:
-            return "y" if (_str_val(expr[1]) == _str_val(expr[2])) else "n"
-
-        if expr[0] == UNEQUAL:
-            return "y" if (_str_val(expr[1]) != _str_val(expr[2])) else "n"
-
-        _internal_error("Internal error while evaluating expression: "
-                        "unknown operation {0}.".format(expr[0]))
-
-    def _eval_min(self, e1, e2):
-        """Returns the minimum value of the two expressions. Equates None with
-        'y'."""
-        e1_eval = self._eval_expr(e1)
-        e2_eval = self._eval_expr(e2)
-        return e1_eval if tri_less(e1_eval, e2_eval) else e2_eval
-
-    def _eval_max(self, e1, e2):
-        """Returns the maximum value of the two expressions. Equates None with
-        'y'."""
-        e1_eval = self._eval_expr(e1)
-        e2_eval = self._eval_expr(e2)
-        return e1_eval if tri_greater(e1_eval, e2_eval) else e2_eval
+        self._parse_error("malformed expression")
 
     #
-    # Dependency tracking (for caching and invalidation)
+    # Caching and invalidation
     #
 
     def _build_dep(self):
-        """Populates the Symbol.dep sets, linking the symbol to the symbols
-        that immediately depend on it in the sense that changing the value of
-        the symbol might affect the values of those other symbols. This is used
-        for caching/invalidation purposes. The calculated sets might be larger
-        than necessary as we don't do any complicated analysis of the
-        expressions."""
+        # Populates the Symbol/Choice._dependents sets, which contain all other
+        # items (symbols and choices) that immediately depend on the item in
+        # the sense that changing the value of the item might affect the value
+        # of the dependent items. This is used for caching/invalidation.
+        #
+        # The calculated sets might be larger than necessary as we don't do any
+        # complex analysis of the expressions.
 
-        # Adds 'sym' as a directly dependent symbol to all symbols that appear
-        # in the expression 'e'
-        def add_expr_deps(e, sym):
-            for s in _get_expr_syms(e):
-                s.dep.add(sym)
+        make_depend_on = _make_depend_on  # Micro-optimization
 
-        # The directly dependent symbols of a symbol are:
-        #  - Any symbols whose prompts, default values, rev_dep (select
-        #    condition), weak_rev_dep (imply condition) or ranges depend on the
-        #    symbol
-        #  - Any symbols that belong to the same choice statement as the symbol
-        #    (these won't be included in 'dep' as that makes the dependency
-        #    graph unwieldy, but Symbol._get_dependent() will include them)
-        #  - Any symbols in a choice statement that depends on the symbol
-        for sym in self.syms_iter():
-            for _, e in sym.prompts:
-                add_expr_deps(e, sym)
+        # Only calculate _dependents for defined symbols. Constant and
+        # undefined symbols could theoretically be selected/implied, but it
+        # wouldn't change their value, so it's not a true dependency.
+        for sym in self.unique_defined_syms:
+            # Symbols depend on the following:
 
-            for v, e in sym.def_exprs:
-                add_expr_deps(v, sym)
-                add_expr_deps(e, sym)
+            # The prompt conditions
+            for node in sym.nodes:
+                if node.prompt:
+                    make_depend_on(sym, node.prompt[1])
 
-            add_expr_deps(sym.rev_dep, sym)
-            add_expr_deps(sym.weak_rev_dep, sym)
+            # The default values and their conditions
+            for value, cond in sym.defaults:
+                make_depend_on(sym, value)
+                make_depend_on(sym, cond)
 
-            for l, u, e in sym.ranges:
-                add_expr_deps(l, sym)
-                add_expr_deps(u, sym)
-                add_expr_deps(e, sym)
+            # The reverse and weak reverse dependencies
+            make_depend_on(sym, sym.rev_dep)
+            make_depend_on(sym, sym.weak_rev_dep)
 
-            if sym.is_choice_sym:
-                choice = sym.parent
-                for _, e in choice.prompts:
-                    add_expr_deps(e, sym)
-                for _, e in choice.def_exprs:
-                    add_expr_deps(e, sym)
+            # The ranges along with their conditions
+            for low, high, cond in sym.ranges:
+                make_depend_on(sym, low)
+                make_depend_on(sym, high)
+                make_depend_on(sym, cond)
 
-    def _eq_to_sym(self, eq):
-        """_expr_depends_on() helper. For (in)equalities of the form sym = y/m
-        or sym != n, returns sym. For other (in)equalities, returns None."""
-        relation, left, right = eq
+            # The direct dependencies. This is usually redundant, as the direct
+            # dependencies get propagated to properties, but it's needed to get
+            # invalidation solid for 'imply', which only checks the direct
+            # dependencies (even if there are no properties to propagate it
+            # to).
+            make_depend_on(sym, sym.direct_dep)
 
-        def transform_y_m_n(item):
-            if item is self.y: return "y"
-            if item is self.m: return "m"
-            if item is self.n: return "n"
-            return item
+            # In addition to the above, choice symbols depend on the choice
+            # they're in, but that's handled automatically since the Choice is
+            # propagated to the conditions of the properties before
+            # _build_dep() runs.
 
-        left = transform_y_m_n(left)
-        right = transform_y_m_n(right)
+        for choice in self.unique_choices:
+            # Choices depend on the following:
 
-        # Make sure the symbol (if any) appears to the left
-        if not isinstance(left, Symbol):
-            left, right = right, left
-        if not isinstance(left, Symbol):
-            return None
-        if (relation == EQUAL and (right == "y" or right == "m")) or \
-           (relation == UNEQUAL and right == "n"):
-            return left
-        return None
+            # The prompt conditions
+            for node in choice.nodes:
+                if node.prompt:
+                    make_depend_on(choice, node.prompt[1])
 
-    def _expr_depends_on(self, expr, sym):
-        """Reimplementation of expr_depends_symbol() from mconf.c. Used to
-        determine if a submenu should be implicitly created, which influences
-        what items inside choice statements are considered choice items."""
-        if expr is None:
-            return False
+            # The default symbol conditions
+            for _, cond in choice.defaults:
+                make_depend_on(choice, cond)
 
-        def rec(expr):
-            if isinstance(expr, str):
-                return False
-            if isinstance(expr, Symbol):
-                return expr is sym
+    def _add_choice_deps(self):
+        # Choices also depend on the choice symbols themselves, because the
+        # y-mode selection of the choice might change if a choice symbol's
+        # visibility changes.
+        #
+        # We add these dependencies separately after dependency loop detection.
+        # The invalidation algorithm can handle the resulting
+        # <choice symbol> <-> <choice> dependency loops, but they make loop
+        # detection awkward.
 
-            if expr[0] in (EQUAL, UNEQUAL):
-                return self._eq_to_sym(expr) is sym
-            if expr[0] == AND:
-                for and_expr in expr[1]:
-                    if rec(and_expr):
-                        return True
-            return False
-
-        return rec(expr)
+        for choice in self.unique_choices:
+            for sym in choice.syms:
+                sym._dependents.add(choice)
 
     def _invalidate_all(self):
-        for sym in self.syms_iter():
+        # Undefined symbols never change value and don't need to be
+        # invalidated, so we can just iterate over defined symbols.
+        # Invalidating constant symbols would break things horribly.
+        for sym in self.unique_defined_syms:
             sym._invalidate()
 
+        for choice in self.unique_choices:
+            choice._invalidate()
+
     #
-    # Printing and misc.
+    # Post-parsing menu tree processing, including dependency propagation and
+    # implicit submenu creation
     #
 
-    def _expand_sym_refs(self, s):
-        """Expands $-references to symbols in 's' to symbol values, or to the
-        empty string for undefined symbols."""
-
-        while 1:
-            sym_ref_match = _sym_ref_re_search(s)
-            if sym_ref_match is None:
-                return s
-
-            sym_name = sym_ref_match.group(0)[1:]
-            sym = self.syms.get(sym_name)
-            expansion = "" if sym is None else sym.get_value()
-
-            s = s[:sym_ref_match.start()] + \
-                expansion + \
-                s[sym_ref_match.end():]
-
-    def _expr_val_str(self, expr, no_value_str="(none)",
-                      get_val_instead_of_eval=False):
-        """Printing helper. Returns a string with 'expr' and its value.
-
-        no_value_str: String to return when 'expr' is missing (None).
-
-        get_val_instead_of_eval: Assume 'expr' is a symbol or string (constant
-          symbol) and get its value directly instead of evaluating it to a
-          tristate value."""
-
-        if expr is None:
-            return no_value_str
-
-        if get_val_instead_of_eval:
-            if isinstance(expr, str):
-                return _expr_to_str(expr)
-            val = expr.get_value()
-        else:
-            val = self._eval_expr(expr)
-
-        return "{0} (value: {1})".format(_expr_to_str(expr), _expr_to_str(val))
-
-    def _get_sym_or_choice_str(self, sc):
-        """Symbols and choices have many properties in common, so we factor out
-        common __str__() stuff here. "sc" is short for "symbol or choice"."""
-
-        # As we deal a lot with string representations here, use some
-        # convenient shorthand:
-        s = _expr_to_str
-
+    def _finalize_node(self, node, visible_if):
+        # Finalizes a menu node and its children:
         #
-        # Common symbol/choice properties
+        #  - Copies properties from menu nodes up to their contained
+        #    symbols/choices
         #
-
-        user_val_str = "(no user value)" if sc.user_val is None else \
-                       s(sc.user_val)
-
-        # Build prompts string
-        if not sc.prompts:
-            prompts_str = " (no prompts)"
-        else:
-            prompts_str_rows = []
-            for prompt, cond_expr in sc.orig_prompts:
-                prompts_str_rows.append(
-                    ' "{0}"'.format(prompt) if cond_expr is None else
-                    ' "{0}" if {1}'.format(prompt,
-                                           self._expr_val_str(cond_expr)))
-            prompts_str = "\n".join(prompts_str_rows)
-
-        # Build locations string
-        locations_str = "(no locations)" if not sc.def_locations else \
-                        " ".join(["{0}:{1}".format(filename, linenr) for
-                                  filename, linenr in sc.def_locations])
-
-        # Build additional-dependencies-from-menus-and-ifs string
-        additional_deps_str = " " + \
-          self._expr_val_str(sc.deps_from_containing,
-                             "(no additional dependencies)")
-
+        #  - Propagates dependencies from parent to child nodes
         #
-        # Symbol-specific stuff
+        #  - Creates implicit menus (see kconfig-language.txt)
         #
+        #  - Removes 'if' nodes
+        #
+        #  - Sets 'choice' types and registers choice symbols
+        #
+        # menu_finalize() in the C implementation is similar.
+        #
+        # node:
+        #   The menu node to finalize. This node and its children will have
+        #   been finalized when the function returns, and any implicit menus
+        #   will have been created.
+        #
+        # visible_if:
+        #   Dependencies from 'visible if' on parent menus. These are added to
+        #   the prompts of symbols and choices.
 
-        if isinstance(sc, Symbol):
-            # Build ranges string
-            if isinstance(sc, Symbol):
-                if not sc.ranges:
-                    ranges_str = " (no ranges)"
+        if node.item.__class__ is Symbol:
+            # Copy defaults, ranges, selects, and implies to the Symbol
+            self._add_props_to_sym(node)
+
+            # Find any items that should go in an implicit menu rooted at the
+            # symbol
+            cur = node
+            while cur.next and _auto_menu_dep(node, cur.next):
+                # This makes implicit submenu creation work recursively, with
+                # implicit menus inside implicit menus
+                self._finalize_node(cur.next, visible_if)
+                cur = cur.next
+                cur.parent = node
+
+            if cur is not node:
+                # Found symbols that should go in an implicit submenu. Tilt
+                # them up above us.
+                node.list = node.next
+                node.next = cur.next
+                cur.next = None
+
+        elif node.list:
+            # The menu node is a choice, menu, or if. Finalize each child node.
+
+            if node.item is MENU:
+                visible_if = self._make_and(visible_if, node.visibility)
+
+            # Propagate the menu node's dependencies to each child menu node.
+            #
+            # This needs to go before the recursive _finalize_node() call so
+            # that implicit submenu creation can look ahead at dependencies.
+            self._propagate_deps(node, visible_if)
+
+            # Finalize the children
+            cur = node.list
+            while cur:
+                self._finalize_node(cur, visible_if)
+                cur = cur.next
+
+        if node.list:
+            # node's children have been individually finalized. Do final steps
+            # to finalize this "level" in the menu tree.
+            _flatten(node.list)
+            _remove_ifs(node)
+
+        # Empty choices (node.list None) are possible, so this needs to go
+        # outside
+        if node.item.__class__ is Choice:
+            # Add the node's non-node-specific properties to the choice, like
+            # _add_props_to_sym() does
+            choice = node.item
+            choice.direct_dep = self._make_or(choice.direct_dep, node.dep)
+            choice.defaults += node.defaults
+
+            _finalize_choice(node)
+
+    def _propagate_deps(self, node, visible_if):
+        # Propagates 'node's dependencies to its child menu nodes
+
+        # If the parent node holds a Choice, we use the Choice itself as the
+        # parent dependency. This makes sense as the value (mode) of the choice
+        # limits the visibility of the contained choice symbols. The C
+        # implementation works the same way.
+        #
+        # Due to the similar interface, Choice works as a drop-in replacement
+        # for Symbol here.
+        basedep = node.item if node.item.__class__ is Choice else node.dep
+
+        cur = node.list
+        while cur:
+            dep = cur.dep = self._make_and(cur.dep, basedep)
+
+            if cur.item.__class__ in _SYMBOL_CHOICE:
+                # Propagate 'visible if' and dependencies to the prompt
+                if cur.prompt:
+                    cur.prompt = (cur.prompt[0],
+                                  self._make_and(
+                                      cur.prompt[1],
+                                      self._make_and(visible_if, dep)))
+
+                # Propagate dependencies to defaults
+                if cur.defaults:
+                    cur.defaults = [(default, self._make_and(cond, dep))
+                                    for default, cond in cur.defaults]
+
+                # Propagate dependencies to ranges
+                if cur.ranges:
+                    cur.ranges = [(low, high, self._make_and(cond, dep))
+                                  for low, high, cond in cur.ranges]
+
+                # Propagate dependencies to selects
+                if cur.selects:
+                    cur.selects = [(target, self._make_and(cond, dep))
+                                   for target, cond in cur.selects]
+
+                # Propagate dependencies to implies
+                if cur.implies:
+                    cur.implies = [(target, self._make_and(cond, dep))
+                                   for target, cond in cur.implies]
+
+            elif cur.prompt:  # Not a symbol/choice
+                # Propagate dependencies to the prompt. 'visible if' is only
+                # propagated to symbols/choices.
+                cur.prompt = (cur.prompt[0],
+                              self._make_and(cur.prompt[1], dep))
+
+            cur = cur.next
+
+    def _add_props_to_sym(self, node):
+        # Copies properties from the menu node 'node' up to its contained
+        # symbol, and adds (weak) reverse dependencies to selected/implied
+        # symbols.
+        #
+        # This can't be rolled into _propagate_deps(), because that function
+        # traverses the menu tree roughly breadth-first, meaning properties on
+        # symbols defined in multiple locations could end up in the wrong
+        # order.
+
+        sym = node.item
+
+        # See the Symbol class docstring
+        sym.direct_dep = self._make_or(sym.direct_dep, node.dep)
+
+        sym.defaults += node.defaults
+        sym.ranges += node.ranges
+        sym.selects += node.selects
+        sym.implies += node.implies
+
+        # Modify the reverse dependencies of the selected symbol
+        for target, cond in node.selects:
+            target.rev_dep = self._make_or(
+                target.rev_dep,
+                self._make_and(sym, cond))
+
+        # Modify the weak reverse dependencies of the implied
+        # symbol
+        for target, cond in node.implies:
+            target.weak_rev_dep = self._make_or(
+                target.weak_rev_dep,
+                self._make_and(sym, cond))
+
+    #
+    # Misc.
+    #
+
+    def _check_sym_sanity(self):
+        # Checks various symbol properties that are handiest to check after
+        # parsing. Only generates errors and warnings.
+
+        def num_ok(sym, type_):
+            # Returns True if the (possibly constant) symbol 'sym' is valid as a value
+            # for a symbol of type type_ (INT or HEX)
+
+            # 'not sym.nodes' implies a constant or undefined symbol, e.g. a plain
+            # "123"
+            if not sym.nodes:
+                return _is_base_n(sym.name, _TYPE_TO_BASE[type_])
+
+            return sym.orig_type is type_
+
+        for sym in self.unique_defined_syms:
+            if sym.orig_type in _BOOL_TRISTATE:
+                # A helper function could be factored out here, but keep it
+                # speedy/straightforward
+
+                for target_sym, _ in sym.selects:
+                    if target_sym.orig_type not in _BOOL_TRISTATE_UNKNOWN:
+                        self._warn("{} selects the {} symbol {}, which is not "
+                                   "bool or tristate"
+                                   .format(_name_and_loc(sym),
+                                           TYPE_TO_STR[target_sym.orig_type],
+                                           _name_and_loc(target_sym)))
+
+                for target_sym, _ in sym.implies:
+                    if target_sym.orig_type not in _BOOL_TRISTATE_UNKNOWN:
+                        self._warn("{} implies the {} symbol {}, which is not "
+                                   "bool or tristate"
+                                   .format(_name_and_loc(sym),
+                                           TYPE_TO_STR[target_sym.orig_type],
+                                           _name_and_loc(target_sym)))
+
+            elif sym.orig_type:  # STRING/INT/HEX
+                for default, _ in sym.defaults:
+                    if default.__class__ is not Symbol:
+                        raise KconfigError(
+                            "the {} symbol {} has a malformed default {} -- expected "
+                            "a single symbol"
+                            .format(TYPE_TO_STR[sym.orig_type], _name_and_loc(sym),
+                                    expr_str(default)))
+
+                    if sym.orig_type is STRING:
+                        if not default.is_constant and not default.nodes and \
+                           not default.name.isupper():
+                            # 'default foo' on a string symbol could be either a symbol
+                            # reference or someone leaving out the quotes. Guess that
+                            # the quotes were left out if 'foo' isn't all-uppercase
+                            # (and no symbol named 'foo' exists).
+                            self._warn("style: quotes recommended around "
+                                       "default value for string symbol "
+                                       + _name_and_loc(sym))
+
+                    elif not num_ok(default, sym.orig_type):  # INT/HEX
+                        self._warn("the {0} symbol {1} has a non-{0} default {2}"
+                                   .format(TYPE_TO_STR[sym.orig_type],
+                                           _name_and_loc(sym),
+                                           _name_and_loc(default)))
+
+                if sym.selects or sym.implies:
+                    self._warn("the {} symbol {} has selects or implies"
+                               .format(TYPE_TO_STR[sym.orig_type],
+                                       _name_and_loc(sym)))
+
+            else:  # UNKNOWN
+                self._warn("{} defined without a type"
+                           .format(_name_and_loc(sym)))
+
+
+            if sym.ranges:
+                if sym.orig_type not in _INT_HEX:
+                    self._warn(
+                        "the {} symbol {} has ranges, but is not int or hex"
+                        .format(TYPE_TO_STR[sym.orig_type],
+                                _name_and_loc(sym)))
                 else:
-                    ranges_str_rows = []
-                    for l, u, cond_expr in sc.ranges:
-                        ranges_str_rows.append(
-                            " [{0}, {1}]".format(s(l), s(u))
-                            if cond_expr is None else
-                            " [{0}, {1}] if {2}"
-                            .format(s(l), s(u), self._expr_val_str(cond_expr)))
-                    ranges_str = "\n".join(ranges_str_rows)
+                    for low, high, _ in sym.ranges:
+                        if not num_ok(low, sym.orig_type) or \
+                           not num_ok(high, sym.orig_type):
 
-            # Build default values string
-            if not sc.def_exprs:
-                defaults_str = " (no default values)"
+                            self._warn("the {0} symbol {1} has a non-{0} "
+                                       "range [{2}, {3}]"
+                                       .format(TYPE_TO_STR[sym.orig_type],
+                                               _name_and_loc(sym),
+                                               _name_and_loc(low),
+                                               _name_and_loc(high)))
+
+    def _check_choice_sanity(self):
+        # Checks various choice properties that are handiest to check after
+        # parsing. Only generates errors and warnings.
+
+        def warn_select_imply(sym, expr, expr_type):
+            msg = "the choice symbol {} is {} by the following symbols, but " \
+                  "select/imply has no effect on choice symbols" \
+                  .format(_name_and_loc(sym), expr_type)
+
+            # si = select/imply
+            for si in split_expr(expr, OR):
+                msg += "\n - " + _name_and_loc(split_expr(si, AND)[0])
+
+            self._warn(msg)
+
+        for choice in self.unique_choices:
+            if choice.orig_type not in _BOOL_TRISTATE:
+                self._warn("{} defined with type {}"
+                           .format(_name_and_loc(choice),
+                                   TYPE_TO_STR[choice.orig_type]))
+
+            for node in choice.nodes:
+                if node.prompt:
+                    break
             else:
-                defaults_str_rows = []
-                for val_expr, cond_expr in sc.orig_def_exprs:
-                    row_str = " " + self._expr_val_str(val_expr, "(none)",
-                                                       sc.type == STRING)
-                    defaults_str_rows.append(row_str)
-                    defaults_str_rows.append("  Condition: " +
-                                               self._expr_val_str(cond_expr))
-                defaults_str = "\n".join(defaults_str_rows)
+                self._warn(_name_and_loc(choice) + " defined without a prompt")
 
-            # Build selects string
-            if not sc.orig_selects:
-                selects_str = " (no selects)"
-            else:
-                selects_str_rows = []
-                for target, cond_expr in sc.orig_selects:
-                    selects_str_rows.append(
-                        " {0}".format(target.name) if cond_expr is None else
-                        " {0} if {1}".format(target.name,
-                                             self._expr_val_str(cond_expr)))
-                selects_str = "\n".join(selects_str_rows)
+            for default, _ in choice.defaults:
+                if default.__class__ is not Symbol:
+                    raise KconfigError(
+                        "{} has a malformed default {}"
+                        .format(_name_and_loc(choice), expr_str(default)))
 
-            # Build implies string
-            if not sc.orig_implies:
-                implies_str = " (no implies)"
-            else:
-                implies_str_rows = []
-                for target, cond_expr in sc.orig_implies:
-                    implies_str_rows.append(
-                        " {0}".format(target.name) if cond_expr is None else
-                        " {0} if {1}".format(target.name,
-                                             self._expr_val_str(cond_expr)))
-                implies_str = "\n".join(implies_str_rows)
+                if default.choice is not choice:
+                    self._warn("the default selection {} of {} is not "
+                               "contained in the choice"
+                               .format(_name_and_loc(default),
+                                       _name_and_loc(choice)))
 
-            res = _lines("Symbol " +
-                           ("(no name)" if sc.name is None else sc.name),
-                         "Type           : " + TYPENAME[sc.type],
-                         "Value          : " + s(sc.get_value()),
-                         "User value     : " + user_val_str,
-                         "Visibility     : " + s(_get_visibility(sc)),
-                         "Is choice item : " + BOOL_STR[sc.is_choice_sym],
-                         "Is defined     : " + BOOL_STR[sc.is_defined_],
-                         "Is from env.   : " + BOOL_STR[sc.is_from_env],
-                         "Is special     : " + BOOL_STR[sc.is_special_] + "\n")
-            if sc.ranges:
-                res += _lines("Ranges:", ranges_str + "\n")
-            res += _lines("Prompts:",
-                          prompts_str,
-                          "Default values:",
-                          defaults_str,
-                          "Selects:",
-                          selects_str,
-                          "Implies:",
-                          implies_str,
-                          "Reverse (select-related) dependencies:",
-                          " (no reverse dependencies)"
-                          if sc.rev_dep == "n"
-                          else " " + self._expr_val_str(sc.rev_dep),
-                          "Weak reverse (imply-related) dependencies:",
-                          " (no weak reverse dependencies)"
-                          if sc.weak_rev_dep == "n"
-                          else " " + self._expr_val_str(sc.weak_rev_dep),
-                          "Additional dependencies from enclosing menus "
-                            "and ifs:",
-                          additional_deps_str,
-                          "Locations: " + locations_str)
+            for sym in choice.syms:
+                if sym.defaults:
+                    self._warn("default on the choice symbol {} will have "
+                               "no effect, as defaults do not affect choice "
+                               "symbols".format(_name_and_loc(sym)))
 
-            return res
+                if sym.rev_dep is not sym.kconfig.n:
+                    warn_select_imply(sym, sym.rev_dep, "selected")
 
+                if sym.weak_rev_dep is not sym.kconfig.n:
+                    warn_select_imply(sym, sym.weak_rev_dep, "implied")
+
+                for node in sym.nodes:
+                    if node.parent.item is choice:
+                        if not node.prompt:
+                            self._warn("the choice symbol {} has no prompt"
+                                       .format(_name_and_loc(sym)))
+
+                    elif node.prompt:
+                        self._warn("the choice symbol {} is defined with a "
+                                   "prompt outside the choice"
+                                   .format(_name_and_loc(sym)))
+
+    def _parse_error(self, msg):
+        raise KconfigError("{}couldn't parse '{}': {}".format(
+            "" if self.filename is None else
+                "{}:{}: ".format(self.filename, self.linenr),
+            self._line.strip(), msg))
+
+    def _trailing_tokens_error(self):
+        self._parse_error("extra tokens at end of line")
+
+    def _open(self, filename, mode):
+        # open() wrapper:
         #
-        # Choice-specific stuff
+        # - Enable universal newlines mode on Python 2 to ease
+        #   interoperability between Linux and Windows. It's already the
+        #   default on Python 3.
         #
+        #   The "U" flag would currently work for both Python 2 and 3, but it's
+        #   deprecated on Python 3, so play it future-safe.
+        #
+        #   io.open() defaults to universal newlines on Python 2 (and is an
+        #   alias for open() on Python 3), but it returns 'unicode' strings and
+        #   slows things down:
+        #
+        #     Parsing x86 Kconfigs on Python 2
+        #
+        #     with open(..., "rU"):
+        #
+        #       real  0m0.930s
+        #       user  0m0.905s
+        #       sys   0m0.025s
+        #
+        #     with io.open():
+        #
+        #       real  0m1.069s
+        #       user  0m1.040s
+        #       sys   0m0.029s
+        #
+        #   There's no appreciable performance difference between "r" and
+        #   "rU" for parsing performance on Python 2.
+        #
+        # - For Python 3, force the encoding. Forcing the encoding on Python 2
+        #   turns strings into Unicode strings, which gets messy. Python 2
+        #   doesn't decode regular strings anyway.
+        return open(filename, "rU" if mode == "r" else mode) if _IS_PY2 else \
+               open(filename, mode, encoding=self._encoding)
 
-        # Build selected symbol string
-        sel = sc.get_selection()
-        sel_str = "(no selection)" if sel is None else sel.name
+    def _check_undef_syms(self):
+        # Prints warnings for all references to undefined symbols within the
+        # Kconfig files
 
-        # Build default values string
-        if not sc.def_exprs:
-            defaults_str = " (no default values)"
-        else:
-            defaults_str_rows = []
-            for sym, cond_expr in sc.orig_def_exprs:
-                defaults_str_rows.append(
-                    " {0}".format(sym.name) if cond_expr is None else
-                    " {0} if {1}".format(sym.name,
-                                         self._expr_val_str(cond_expr)))
-            defaults_str = "\n".join(defaults_str_rows)
+        def is_num(s):
+            # Returns True if the string 's' looks like a number.
+            #
+            # Internally, all operands in Kconfig are symbols, only undefined symbols
+            # (which numbers usually are) get their name as their value.
+            #
+            # Only hex numbers that start with 0x/0X are classified as numbers.
+            # Otherwise, symbols whose names happen to contain only the letters A-F
+            # would trigger false positives.
 
-        # Build contained symbols string
-        names = [sym.name for sym in sc.actual_symbols]
-        syms_string = " ".join(names) if names else "(empty)"
+            try:
+                int(s)
+            except ValueError:
+                if not s.startswith(("0x", "0X")):
+                    return False
 
-        return _lines("Choice",
-                      "Name (for named choices): " +
-                        ("(no name)" if sc.name is None else sc.name),
-                      "Type            : " + TYPENAME[sc.type],
-                      "Selected symbol : " + sel_str,
-                      "User value      : " + user_val_str,
-                      "Mode            : " + s(sc.get_mode()),
-                      "Visibility      : " + s(_get_visibility(sc)),
-                      "Optional        : " + BOOL_STR[sc.optional],
-                      "Prompts:",
-                      prompts_str,
-                      "Defaults:",
-                      defaults_str,
-                      "Choice symbols:",
-                      " " + syms_string,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Locations: " + locations_str)
+                try:
+                    int(s, 16)
+                except ValueError:
+                    return False
+
+            return True
+
+        for sym in (self.syms.viewvalues if _IS_PY2 else self.syms.values)():
+            # - sym.nodes empty means the symbol is undefined (has no
+            #   definition locations)
+            #
+            # - Due to Kconfig internals, numbers show up as undefined Kconfig
+            #   symbols, but shouldn't be flagged
+            #
+            # - The MODULES symbol always exists
+            if not sym.nodes and not is_num(sym.name) and \
+               sym.name != "MODULES":
+
+                msg = "undefined symbol {}:".format(sym.name)
+                for node in self.node_iter():
+                    if sym in node.referenced:
+                        msg += "\n\n- Referenced at {}:{}:\n\n{}" \
+                               .format(node.filename, node.linenr, node)
+                self._warn(msg)
 
     def _warn(self, msg, filename=None, linenr=None):
-        """For printing warnings to stderr."""
-        msg = _build_msg("warning: " + msg, filename, linenr)
-        if self.print_warnings:
+        # For printing general warnings
+
+        if not self.warn:
+            return
+
+        msg = "warning: " + msg
+        if filename is not None:
+            msg = "{}:{}: {}".format(filename, linenr, msg)
+
+        self.warnings.append(msg)
+        if self.warn_to_stderr:
             sys.stderr.write(msg + "\n")
-        self._warnings.append(msg)
 
-class Item(object):
 
-    """Base class for symbols and other Kconfig constructs. Subclasses are
-    Symbol, Choice, Menu, and Comment."""
+class Symbol(object):
+    """
+    Represents a configuration symbol:
 
-    def is_symbol(self):
-        """Returns True if the item is a symbol. Short for
-        isinstance(item, kconfiglib.Symbol)."""
-        return isinstance(self, Symbol)
+      (menu)config FOO
+          ...
 
-    def is_choice(self):
-        """Returns True if the item is a choice. Short for
-        isinstance(item, kconfiglib.Choice)."""
-        return isinstance(self, Choice)
+    The following attributes are available. They should be viewed as read-only,
+    and some are implemented through @property magic (but are still efficient
+    to access due to internal caching).
 
-    def is_menu(self):
-        """Returns True if the item is a menu. Short for
-        isinstance(item, kconfiglib.Menu)."""
-        return isinstance(self, Menu)
+    Note: Prompts, help texts, and locations are stored in the Symbol's
+    MenuNode(s) rather than in the Symbol itself. Check the MenuNode class and
+    the Symbol.nodes attribute. This organization matches the C tools.
 
-    def is_comment(self):
-        """Returns True if the item is a comment. Short for
-        isinstance(item, kconfiglib.Comment)."""
-        return isinstance(self, Comment)
+    name:
+      The name of the symbol, e.g. "FOO" for 'config FOO'.
 
-class Symbol(Item):
+    type:
+      The type of the symbol. One of BOOL, TRISTATE, STRING, INT, HEX, UNKNOWN.
+      UNKNOWN is for undefined symbols, (non-special) constant symbols, and
+      symbols defined without a type.
 
-    """Represents a configuration symbol - e.g. FOO for
+      When running without modules (MODULES having the value n), TRISTATE
+      symbols magically change type to BOOL. This also happens for symbols
+      within choices in "y" mode. This matches the C tools, and makes sense for
+      menuconfig-like functionality.
 
-    config FOO
-        ..."""
+    orig_type:
+      The type as given in the Kconfig file, without any magic applied. Used
+      when printing the symbol.
+
+    str_value:
+      The value of the symbol as a string. Gives the value for string/int/hex
+      symbols. For bool/tristate symbols, gives "n", "m", or "y".
+
+      This is the symbol value that's used in relational expressions
+      (A = B, A != B, etc.)
+
+      Gotcha: For int/hex symbols, the exact format of the value must often be
+      preserved (e.g., when writing a .config file), hence why you can't get it
+      directly as an int. Do int(int_sym.str_value) or
+      int(hex_sym.str_value, 16) to get the integer value.
+
+    tri_value:
+      The tristate value of the symbol as an integer. One of 0, 1, 2,
+      representing n, m, y. Always 0 (n) for non-bool/tristate symbols.
+
+      This is the symbol value that's used outside of relation expressions
+      (A, !A, A && B, A || B).
+
+    assignable:
+      A tuple containing the tristate user values that can currently be
+      assigned to the symbol (that would be respected), ordered from lowest (0,
+      representing n) to highest (2, representing y). This corresponds to the
+      selections available in the menuconfig interface. The set of assignable
+      values is calculated from the symbol's visibility and selects/implies.
+
+      Returns the empty set for non-bool/tristate symbols and for symbols with
+      visibility n. The other possible values are (0, 2), (0, 1, 2), (1, 2),
+      (1,), and (2,). A (1,) or (2,) result means the symbol is visible but
+      "locked" to m or y through a select, perhaps in combination with the
+      visibility. menuconfig represents this as -M- and -*-, respectively.
+
+      For string/hex/int symbols, check if Symbol.visibility is non-0 (non-n)
+      instead to determine if the value can be changed.
+
+      Some handy 'assignable' idioms:
+
+        # Is 'sym' an assignable (visible) bool/tristate symbol?
+        if sym.assignable:
+            # What's the highest value it can be assigned? [-1] in Python
+            # gives the last element.
+            sym_high = sym.assignable[-1]
+
+            # The lowest?
+            sym_low = sym.assignable[0]
+
+            # Can the symbol be set to at least m?
+            if sym.assignable[-1] >= 1:
+                ...
+
+        # Can the symbol be set to m?
+        if 1 in sym.assignable:
+            ...
+
+    visibility:
+      The visibility of the symbol. One of 0, 1, 2, representing n, m, y. See
+      the module documentation for an overview of symbol values and visibility.
+
+    user_value:
+      The user value of the symbol. None if no user value has been assigned
+      (via Kconfig.load_config() or Symbol.set_value()).
+
+      Holds 0, 1, or 2 for bool/tristate symbols, and a string for the other
+      symbol types.
+
+      WARNING: Do not assign directly to this. It will break things. Use
+      Symbol.set_value().
+
+    config_string:
+      The .config assignment string that would get written out for the symbol
+      by Kconfig.write_config(). Returns the empty string if no .config
+      assignment would get written out.
+
+      In general, visible symbols, symbols with (active) defaults, and selected
+      symbols get written out. This includes all non-n-valued bool/tristate
+      symbols, and all visible string/int/hex symbols.
+
+      Symbols with the (no longer needed) 'option env=...' option generate no
+      configuration output, and neither does the special
+      'option defconfig_list' symbol.
+
+      Tip: This field is useful when generating custom configuration output,
+      even for non-.config-like formats. To write just the symbols that would
+      get written out to .config files, do this:
+
+        if sym.config_string:
+            *Write symbol, e.g. by looking sym.str_value*
+
+      This is a superset of the symbols written out by write_autoconf().
+      That function skips all n-valued symbols.
+
+      There usually won't be any great harm in just writing all symbols either,
+      though you might get some special symbols and possibly some "redundant"
+      n-valued symbol entries in there.
+
+    nodes:
+      A list of MenuNodes for this symbol. Will contain a single MenuNode for
+      most symbols. Undefined and constant symbols have an empty nodes list.
+      Symbols defined in multiple locations get one node for each location.
+
+    choice:
+      Holds the parent Choice for choice symbols, and None for non-choice
+      symbols. Doubles as a flag for whether a symbol is a choice symbol.
+
+    defaults:
+      List of (default, cond) tuples for the symbol's 'default' properties. For
+      example, 'default A && B if C || D' is represented as
+      ((AND, A, B), (OR, C, D)). If no condition was given, 'cond' is
+      self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to
+      'default' conditions.
+
+    selects:
+      List of (symbol, cond) tuples for the symbol's 'select' properties. For
+      example, 'select A if B && C' is represented as (A, (AND, B, C)). If no
+      condition was given, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to 'select'
+      conditions.
+
+    implies:
+      Like 'selects', for imply.
+
+    ranges:
+      List of (low, high, cond) tuples for the symbol's 'range' properties. For
+      example, 'range 1 2 if A' is represented as (1, 2, A). If there is no
+      condition, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to 'range'
+      conditions.
+
+      Gotcha: 1 and 2 above will be represented as (undefined) Symbols rather
+      than plain integers. Undefined symbols get their name as their string
+      value, so this works out. The C tools work the same way.
+
+    orig_defaults:
+    orig_selects:
+    orig_implies:
+    orig_ranges:
+      See the corresponding attributes on the MenuNode class.
+
+    rev_dep:
+      Reverse dependency expression from other symbols selecting this symbol.
+      Multiple selections get ORed together. A condition on a select is ANDed
+      with the selecting symbol.
+
+      For example, if A has 'select FOO' and B has 'select FOO if C', then
+      FOO's rev_dep will be (OR, A, (AND, B, C)).
+
+    weak_rev_dep:
+      Like rev_dep, for imply.
+
+    direct_dep:
+      The direct ('depends on') dependencies for the symbol, or self.kconfig.y
+      if there are no direct dependencies.
+
+      This attribute includes any dependencies from surrounding menus and ifs.
+      Those get propagated to the direct dependencies, and the resulting direct
+      dependencies in turn get propagated to the conditions of all properties.
+
+      If the symbol is defined in multiple locations, the dependencies from the
+      different locations get ORed together.
+
+    referenced:
+      A set() with all symbols and choices referenced in the properties and
+      property conditions of the symbol.
+
+      Also includes dependencies from surrounding menus and ifs, because those
+      get propagated to the symbol (see the 'Intro to symbol values' section in
+      the module docstring).
+
+      Choices appear in the dependencies of choice symbols.
+
+      For the following definitions, only B and not C appears in A's
+      'referenced'. To get transitive references, you'll have to recursively
+      expand 'references' until no new items appear.
+
+        config A
+                bool
+                depends on B
+
+        config B
+                bool
+                depends on C
+
+        config C
+                bool
+
+      See the Symbol.direct_dep attribute if you're only interested in the
+      direct dependencies of the symbol (its 'depends on'). You can extract the
+      symbols in it with the global expr_items() function.
+
+    env_var:
+      If the Symbol has an 'option env="FOO"' option, this contains the name
+      ("FOO") of the environment variable. None for symbols without no
+      'option env'.
+
+      'option env="FOO"' acts like a 'default' property whose value is the
+      value of $FOO.
+
+      Symbols with 'option env' are never written out to .config files, even if
+      they are visible. env_var corresponds to a flag called SYMBOL_AUTO in the
+      C implementation.
+
+    is_allnoconfig_y:
+      True if the symbol has 'option allnoconfig_y' set on it. This has no
+      effect internally (except when printing symbols), but can be checked by
+      scripts.
+
+    is_constant:
+      True if the symbol is a constant (quoted) symbol.
+
+    kconfig:
+      The Kconfig instance this symbol is from.
+    """
+    __slots__ = (
+        "_cached_assignable",
+        "_cached_str_val",
+        "_cached_tri_val",
+        "_cached_vis",
+        "_dependents",
+        "_old_val",
+        "_visited",
+        "_was_set",
+        "_write_to_conf",
+        "choice",
+        "defaults",
+        "direct_dep",
+        "env_var",
+        "implies",
+        "is_allnoconfig_y",
+        "is_constant",
+        "kconfig",
+        "name",
+        "nodes",
+        "orig_type",
+        "ranges",
+        "rev_dep",
+        "selects",
+        "user_value",
+        "weak_rev_dep",
+    )
 
     #
     # Public interface
     #
 
-    def get_config(self):
-        """Returns the Config instance this symbol is from."""
-        return self.config
-
-    def get_name(self):
-        """Returns the name of the symbol."""
-        return self.name
-
-    def get_type(self):
-        """Returns the type of the symbol: one of UNKNOWN, BOOL, TRISTATE,
-        STRING, HEX, or INT. These are defined at the top level of the module,
-        so you'd do something like
-
-        if sym.get_type() == kconfiglib.STRING:
-            ..."""
-        return self.type
-
-    def get_prompts(self):
-        """Returns a list of prompts defined for the symbol, in the order they
-        appear in the configuration files. Returns the empty list for symbols
-        with no prompt.
-
-        This list will have a single entry for the vast majority of symbols
-        having prompts, but having multiple prompts for a single symbol is
-        possible through having multiple 'config' entries for it."""
-        return [prompt for prompt, _ in self.orig_prompts]
-
-    def get_help(self):
-        """Returns the help text of the symbol, or None if the symbol has no
-        help text."""
-        return self.help
-
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the symbol, or
-        None if the symbol is at the top level. Note that if statements are
-        treated as syntactic and do not have an explicit class
-        representation."""
-        return self.parent
-
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is defined. For
-        the vast majority of symbols this list will only contain one element.
-        For the following Kconfig, FOO would get two entries: the lines marked
-        with *.
-
-        config FOO *
-            bool "foo prompt 1"
-
-        config FOO *
-            bool "foo prompt 2"
+    @property
+    def type(self):
         """
-        return self.def_locations
-
-    def get_ref_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is referenced in
-        the configuration. For example, the lines marked by * would be included
-        for FOO below:
-
-        config A
-            bool
-            default BAR || FOO *
-
-        config B
-            tristate
-            depends on FOO *
-            default m if FOO *
-
-        if FOO *
-            config A
-                bool "A"
-        endif
-
-        config FOO (definition not included)
-            bool
+        See the class documentation.
         """
-        return self.ref_locations
+        if self.orig_type is TRISTATE and \
+           (self.choice and self.choice.tri_value == 2 or
+            not self.kconfig.modules.tri_value):
 
-    def get_value(self):
-        """Calculate and return the value of the symbol. See also
-        Symbol.set_user_value()."""
+            return BOOL
 
-        if self.cached_val is not None:
-            return self.cached_val
+        return self.orig_type
+
+    @property
+    def str_value(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_str_val is not None:
+            return self._cached_str_val
+
+        if self.orig_type in _BOOL_TRISTATE:
+            # Also calculates the visibility, so invalidation safe
+            self._cached_str_val = TRI_TO_STR[self.tri_value]
+            return self._cached_str_val
 
         # As a quirk of Kconfig, undefined symbols get their name as their
-        # value. This is why things like "FOO = bar" work for seeing if FOO has
-        # the value "bar".
-        if self.type == UNKNOWN:
-            self.cached_val = self.name
+        # string value. This is why things like "FOO = bar" work for seeing if
+        # FOO has the value "bar".
+        if not self.orig_type:  # UNKNOWN
+            self._cached_str_val = self.name
             return self.name
 
-        new_val = DEFAULT_VALUE[self.type]
-        vis = _get_visibility(self)
+        val = ""
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
 
-        # This is easiest to calculate together with the value
-        self.write_to_conf = False
+        self._write_to_conf = (vis != 0)
 
-        if self.type == BOOL or self.type == TRISTATE:
-            # The visibility and mode (modules-only or single-selection) of
-            # choice items will be taken into account in _get_visibility()
-            if self.is_choice_sym:
-                if vis != "n":
-                    choice = self.parent
-                    mode = choice.get_mode()
+        if self.orig_type in _INT_HEX:
+            # The C implementation checks the user value against the range in a
+            # separate code path (post-processing after loading a .config).
+            # Checking all values here instead makes more sense for us. It
+            # requires that we check for a range first.
 
-                    self.write_to_conf = (mode != "n")
+            base = _TYPE_TO_BASE[self.orig_type]
 
-                    if mode == "y":
-                        new_val = "y" if choice.get_selection() is self \
-                                  else "n"
-                    elif mode == "m":
-                        if self.user_val == "m" or self.user_val == "y":
-                            new_val = "m"
-
-            else:
-                # If the symbol is visible and has a user value, use that.
-                # Otherwise, look at defaults and weak reverse dependencies
-                # (implies).
-                use_defaults_and_weak_rev_deps = True
-
-                if vis != "n":
-                    self.write_to_conf = True
-                    if self.user_val is not None:
-                        new_val = self.config._eval_min(self.user_val, vis)
-                        use_defaults_and_weak_rev_deps = False
-
-                if use_defaults_and_weak_rev_deps:
-                    for val_expr, cond_expr in self.def_exprs:
-                        cond_eval = self.config._eval_expr(cond_expr)
-                        if cond_eval != "n":
-                            self.write_to_conf = True
-                            new_val = self.config._eval_min(val_expr,
-                                                            cond_eval)
-                            break
-
-                    weak_rev_dep_val = \
-                        self.config._eval_expr(self.weak_rev_dep)
-                    if weak_rev_dep_val != "n":
-                        self.write_to_conf = True
-                        new_val = self.config._eval_max(new_val,
-                                                        weak_rev_dep_val)
-
-                # Reverse (select-related) dependencies take precedence
-                rev_dep_val = self.config._eval_expr(self.rev_dep)
-                if rev_dep_val != "n":
-                    self.write_to_conf = True
-                    new_val = self.config._eval_max(new_val, rev_dep_val)
-
-            # We need to promote "m" to "y" in two circumstances:
-            #  1) If our type is boolean
-            #  2) If our weak_rev_dep (from IMPLY) is "y"
-            if new_val == "m" and \
-               (self.type == BOOL or
-                self.config._eval_expr(self.weak_rev_dep) == "y"):
-                new_val = "y"
-
-        elif self.type == INT or self.type == HEX:
-            has_active_range = False
-            low = None
-            high = None
-            use_defaults = True
-
-            base = 16 if self.type == HEX else 10
-
-            for l, h, cond_expr in self.ranges:
-                if self.config._eval_expr(cond_expr) != "n":
+            # Check if a range is in effect
+            for low_expr, high_expr, cond in self.ranges:
+                if expr_value(cond):
                     has_active_range = True
 
-                    low_str = _str_val(l)
-                    high_str = _str_val(h)
-                    low = int(low_str, base) if \
-                      _is_base_n(low_str, base) else 0
-                    high = int(high_str, base) if \
-                      _is_base_n(high_str, base) else 0
+                    # The zeros are from the C implementation running strtoll()
+                    # on empty strings
+                    low = int(low_expr.str_value, base) if \
+                      _is_base_n(low_expr.str_value, base) else 0
+                    high = int(high_expr.str_value, base) if \
+                      _is_base_n(high_expr.str_value, base) else 0
 
                     break
+            else:
+                has_active_range = False
 
-            if vis != "n":
-                self.write_to_conf = True
-
-                if self.user_val is not None and \
-                   _is_base_n(self.user_val, base) and \
-                   (not has_active_range or
-                    low <= int(self.user_val, base) <= high):
-
-                    # If the user value is OK, it is stored in exactly the same
-                    # form as specified in the assignment (with or without
-                    # "0x", etc).
-
-                    use_defaults = False
-                    new_val = self.user_val
-
-            if use_defaults:
-                for val_expr, cond_expr in self.def_exprs:
-                    if self.config._eval_expr(cond_expr) != "n":
-                        self.write_to_conf = True
-
-                        # If the default value is OK, it is stored in exactly
-                        # the same form as specified. Otherwise, it is clamped
-                        # to the range, and the output has "0x" as appropriate
-                        # for the type.
-
-                        new_val = _str_val(val_expr)
-
-                        if _is_base_n(new_val, base):
-                            new_val_num = int(new_val, base)
-                            if has_active_range:
-                                clamped_val = None
-
-                                if new_val_num < low:
-                                    clamped_val = low
-                                elif new_val_num > high:
-                                    clamped_val = high
-
-                                if clamped_val is not None:
-                                    new_val = (hex(clamped_val) if \
-                                      self.type == HEX else str(clamped_val))
-
-                            break
-                else: # For the for loop
-                    # If no user value or default kicks in but the hex/int has
-                    # an active range, then the low end of the range is used,
-                    # provided it's > 0, with "0x" prepended as appropriate.
-                    if has_active_range and low > 0:
-                        new_val = (hex(low) if self.type == HEX else str(low))
-
-        elif self.type == STRING:
+            # Defaults are used if the symbol is invisible, lacks a user value,
+            # or has an out-of-range user value
             use_defaults = True
 
-            if vis != "n":
-                self.write_to_conf = True
-                if self.user_val is not None:
-                    new_val = self.user_val
+            if vis and self.user_value:
+                user_val = int(self.user_value, base)
+                if has_active_range and not low <= user_val <= high:
+                    num2str = str if base == 10 else hex
+                    self.kconfig._warn(
+                        "user value {} on the {} symbol {} ignored due to "
+                        "being outside the active range ([{}, {}]) -- falling "
+                        "back on defaults"
+                        .format(num2str(user_val), TYPE_TO_STR[self.orig_type],
+                                _name_and_loc(self),
+                                num2str(low), num2str(high)))
+                else:
+                    # If the user value is well-formed and satisfies range
+                    # contraints, it is stored in exactly the same form as
+                    # specified in the assignment (with or without "0x", etc.)
+                    val = self.user_value
                     use_defaults = False
 
             if use_defaults:
-                for val_expr, cond_expr in self.def_exprs:
-                    if self.config._eval_expr(cond_expr) != "n":
-                        self.write_to_conf = True
-                        new_val = _str_val(val_expr)
+                # No user value or invalid user value. Look at defaults.
+
+                # Used to implement the warning below
+                has_default = False
+
+                for sym, cond in self.defaults:
+                    if expr_value(cond):
+                        has_default = self._write_to_conf = True
+
+                        val = sym.str_value
+
+                        if _is_base_n(val, base):
+                            val_num = int(val, base)
+                        else:
+                            val_num = 0  # strtoll() on empty string
+
+                        break
+                else:
+                    val_num = 0  # strtoll() on empty string
+
+                # This clamping procedure runs even if there's no default
+                if has_active_range:
+                    clamp = None
+                    if val_num < low:
+                        clamp = low
+                    elif val_num > high:
+                        clamp = high
+
+                    if clamp is not None:
+                        # The value is rewritten to a standard form if it is
+                        # clamped
+                        val = str(clamp) \
+                              if self.orig_type is INT else \
+                              hex(clamp)
+
+                        if has_default:
+                            num2str = str if base == 10 else hex
+                            self.kconfig._warn(
+                                "default value {} on {} clamped to {} due to "
+                                "being outside the active range ([{}, {}])"
+                                .format(val_num, _name_and_loc(self),
+                                        num2str(clamp), num2str(low),
+                                        num2str(high)))
+
+        elif self.orig_type is STRING:
+            if vis and self.user_value is not None:
+                # If the symbol is visible and has a user value, use that
+                val = self.user_value
+            else:
+                # Otherwise, look at defaults
+                for sym, cond in self.defaults:
+                    if expr_value(cond):
+                        val = sym.str_value
+                        self._write_to_conf = True
                         break
 
-        self.cached_val = new_val
-        return new_val
+        # env_var corresponds to SYMBOL_AUTO in the C implementation, and is
+        # also set on the defconfig_list symbol there. Test for the
+        # defconfig_list symbol explicitly instead here, to avoid a nonsensical
+        # env_var setting and the defconfig_list symbol being printed
+        # incorrectly. This code is pretty cold anyway.
+        if self.env_var is not None or self is self.kconfig.defconfig_list:
+            self._write_to_conf = False
 
-    def get_user_value(self):
-        """Returns the value assigned to the symbol in a .config or via
-        Symbol.set_user_value() (provided the value was valid for the type of
-        the symbol). Returns None in case of no user value."""
-        return self.user_val
+        self._cached_str_val = val
+        return val
 
-    def get_upper_bound(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns None.
+    @property
+    def tri_value(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_tri_val is not None:
+            return self._cached_tri_val
 
-        Otherwise, returns the highest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "m" or
-        "y", arranged from lowest to highest. This corresponds to the highest
-        value the symbol could be given in e.g. the 'make menuconfig'
-        interface.
+        if self.orig_type not in _BOOL_TRISTATE:
+            if self.orig_type:  # != UNKNOWN
+                # Would take some work to give the location here
+                self.kconfig._warn(
+                    "The {} symbol {} is being evaluated in a logical context "
+                    "somewhere. It will always evaluate to n."
+                    .format(TYPE_TO_STR[self.orig_type], _name_and_loc(self)))
 
-        See also the tri_less*() and tri_greater*() functions, which could come
-        in handy."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return None
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return None
-        vis = _get_visibility(self)
-        if TRI_TO_INT[vis] > TRI_TO_INT[rev_dep]:
-            return vis
-        return None
+            self._cached_tri_val = 0
+            return 0
 
-    def get_lower_bound(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns None.
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+        self._write_to_conf = (vis != 0)
 
-        Otherwise, returns the lowest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "n" or
-        "m", arranged from lowest to highest. This corresponds to the lowest
-        value the symbol could be given in e.g. the 'make menuconfig'
-        interface.
+        val = 0
 
-        See also the tri_less*() and tri_greater*() functions, which could come
-        in handy."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return None
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return None
-        if TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]:
-            return rev_dep
-        return None
+        if not self.choice:
+            # Non-choice symbol
 
-    def get_assignable_values(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns the empty list.
+            if vis and self.user_value is not None:
+                # If the symbol is visible and has a user value, use that
+                val = min(self.user_value, vis)
 
-        Otherwise, returns a list containing the user values that can be
-        assigned to the symbol (that won't be truncated). Usage example:
+            else:
+                # Otherwise, look at defaults and weak reverse dependencies
+                # (implies)
 
-        if "m" in sym.get_assignable_values():
-            sym.set_user_value("m")
+                for default, cond in self.defaults:
+                    dep_val = expr_value(cond)
+                    if dep_val:
+                        val = min(expr_value(default), dep_val)
+                        if val:
+                            self._write_to_conf = True
+                        break
 
-        This is basically a more convenient interface to
-        get_lower/upper_bound() when wanting to test if a particular tristate
-        value can be assigned."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return []
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return []
-        res = ["n", "m", "y"][TRI_TO_INT[rev_dep] :
-                              TRI_TO_INT[_get_visibility(self)] + 1]
-        return res if len(res) > 1 else []
+                # Weak reverse dependencies are only considered if our
+                # direct dependencies are met
+                dep_val = expr_value(self.weak_rev_dep)
+                if dep_val and expr_value(self.direct_dep):
+                    val = max(dep_val, val)
+                    self._write_to_conf = True
 
-    def get_visibility(self):
-        """Returns the visibility of the symbol: one of "n", "m" or "y". For
-        bool and tristate symbols, this is an upper bound on the value users
-        can set for the symbol. For other types of symbols, a visibility of "n"
-        means the user value will be ignored. A visibility of "n" corresponds
-        to not being visible in the 'make *config' interfaces.
+            # Reverse (select-related) dependencies take precedence
+            dep_val = expr_value(self.rev_dep)
+            if dep_val:
+                if expr_value(self.direct_dep) < dep_val:
+                    self._warn_select_unsatisfied_deps()
 
-        Example (assuming we're running with modules enabled -- i.e., MODULES
-        set to 'y'):
+                val = max(dep_val, val)
+                self._write_to_conf = True
 
-        # Assume this has been assigned 'n'
-        config N_SYM
-            tristate "N_SYM"
+            # m is promoted to y for (1) bool symbols and (2) symbols with a
+            # weak_rev_dep (from imply) of y
+            if val == 1 and \
+               (self.type is BOOL or expr_value(self.weak_rev_dep) == 2):
+                val = 2
 
-        # Assume this has been assigned 'm'
-        config M_SYM
-            tristate "M_SYM"
+        elif vis == 2:
+            # Visible choice symbol in y-mode choice. The choice mode limits
+            # the visibility of choice symbols, so it's sufficient to just
+            # check the visibility of the choice symbols themselves.
+            val = 2 if self.choice.selection is self else 0
 
-        # Has visibility 'n'
-        config A
-            tristate "A"
-            depends on N_SYM
+        elif vis and self.user_value:
+            # Visible choice symbol in m-mode choice, with set non-0 user value
+            val = 1
 
-        # Has visibility 'm'
-        config B
-            tristate "B"
-            depends on M_SYM
+        self._cached_tri_val = val
+        return val
 
-        # Has visibility 'y'
-        config C
-            tristate "C"
+    @property
+    def assignable(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_assignable is None:
+            self._cached_assignable = self._assignable()
+        return self._cached_assignable
 
-        # Has no prompt, and hence visibility 'n'
-        config D
-            tristate
+    @property
+    def visibility(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_vis is None:
+            self._cached_vis = _visibility(self)
+        return self._cached_vis
 
-        Having visibility be tri-valued ensures that e.g. a symbol cannot be
-        set to "y" by the user if it depends on a symbol with value "m", which
-        wouldn't be safe.
+    @property
+    def config_string(self):
+        """
+        See the class documentation.
+        """
+        # _write_to_conf is determined when the value is calculated. This is a
+        # hidden function call due to property magic.
+        val = self.str_value
+        if not self._write_to_conf:
+            return ""
 
-        You should probably look at get_lower/upper_bound(),
-        get_assignable_values() and is_modifiable() before using this."""
-        return _get_visibility(self)
+        if self.orig_type in _BOOL_TRISTATE:
+            return "{}{}={}\n" \
+                   .format(self.kconfig.config_prefix, self.name, val) \
+                   if val != "n" else \
+                   "# {}{} is not set\n" \
+                   .format(self.kconfig.config_prefix, self.name)
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """Returns the set() of all symbols referenced by this symbol. For
-        example, the symbol defined by
+        if self.orig_type in _INT_HEX:
+            return "{}{}={}\n" \
+                   .format(self.kconfig.config_prefix, self.name, val)
 
-        config FOO
-            bool
-            prompt "foo" if A && B
-            default C if D
-            depends on E
-            select F if G
+        # sym.orig_type is STRING
+        return '{}{}="{}"\n' \
+               .format(self.kconfig.config_prefix, self.name, escape(val))
 
-        references the symbols A through G.
-
-        refs_from_enclosing (default: False): If True, the symbols referenced
-           by enclosing menus and ifs will be included in the result."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
-
-    def get_selected_symbols(self):
-        """Returns the set() of all symbols X for which this symbol has a
-        'select X' or 'select X if Y' (regardless of whether Y is satisfied or
-        not). This is a subset of the symbols returned by
-        get_referenced_symbols()."""
-        return self.selected_syms
-
-    def get_implied_symbols(self):
-        """Returns the set() of all symbols X for which this symbol has an
-        'imply X' or 'imply X if Y' (regardless of whether Y is satisfied or
-        not). This is a subset of the symbols returned by
-        get_referenced_symbols()."""
-        return self.implied_syms
-
-    def set_user_value(self, v):
-        """Sets the user value of the symbol.
+    def set_value(self, value):
+        """
+        Sets the user value of the symbol.
 
         Equal in effect to assigning the value to the symbol within a .config
-        file. Use get_lower/upper_bound() or get_assignable_values() to find
-        the range of currently assignable values for bool and tristate symbols;
-        setting values outside this range will cause the user value to differ
-        from the result of Symbol.get_value() (be truncated). Values that are
-        invalid for the type (such as a_bool.set_user_value("foo")) are
-        ignored, and a warning is emitted if an attempt is made to assign such
-        a value.
+        file. For bool and tristate symbols, use the 'assignable' attribute to
+        check which values can currently be assigned. Setting values outside
+        'assignable' will cause Symbol.user_value to differ from
+        Symbol.str/tri_value (be truncated down or up).
 
-        For any type of symbol, is_modifiable() can be used to check if a user
-        value will currently have any effect on the symbol, as determined by
-        its visibility and range of assignable values. Any value that is valid
-        for the type (bool, tristate, etc.) will end up being reflected in
-        get_user_value() though, and might have an effect later if conditions
-        change. To get rid of the user value, use unset_user_value().
+        Setting a choice symbol to 2 (y) sets Choice.user_selection to the
+        choice symbol in addition to setting Symbol.user_value.
+        Choice.user_selection is considered when the choice is in y mode (the
+        "normal" mode).
 
-        Any symbols dependent on the symbol are (recursively) invalidated, so
-        things will just work with regards to dependencies.
+        Other symbols that depend (possibly indirectly) on this symbol are
+        automatically recalculated to reflect the assigned value.
 
-        v: The user value to give to the symbol."""
-        self._set_user_value_no_invalidate(v, False)
+        value:
+          The user value to give to the symbol. For bool and tristate symbols,
+          n/m/y can be specified either as 0/1/2 (the usual format for tristate
+          values in Kconfiglib) or as one of the strings "n"/"m"/"y". For other
+          symbol types, pass a string.
 
-        # There might be something more efficient you could do here, but play
-        # it safe.
-        if self.name == "MODULES":
-            self.config._invalidate_all()
-            return
+          Note that the value for an int/hex symbol is passed as a string, e.g.
+          "123" or "0x0123". The format of this string is preserved in the
+          output.
 
-        self._invalidate()
-        self._invalidate_dependent()
+          Values that are invalid for the type (such as "foo" or 1 (m) for a
+          BOOL or "0x123" for an INT) are ignored and won't be stored in
+          Symbol.user_value. Kconfiglib will print a warning by default for
+          invalid assignments, and set_value() will return False.
 
-    def unset_user_value(self):
-        """Resets the user value of the symbol, as if the symbol had never
-        gotten a user value via Config.load_config() or
-        Symbol.set_user_value()."""
-        self._unset_user_value_no_recursive_invalidate()
-        self._invalidate_dependent()
+        Returns True if the value is valid for the type of the symbol, and
+        False otherwise. This only looks at the form of the value. For BOOL and
+        TRISTATE symbols, check the Symbol.assignable attribute to see what
+        values are currently in range and would actually be reflected in the
+        value of the symbol. For other symbol types, check whether the
+        visibility is non-n.
+        """
+        if self.orig_type in _BOOL_TRISTATE and value in STR_TO_TRI:
+            value = STR_TO_TRI[value]
 
-    def is_modifiable(self):
-        """Returns True if the value of the symbol could be modified by calling
-        Symbol.set_user_value().
-
-        For bools and tristates, this corresponds to the symbol being visible
-        in the 'make menuconfig' interface and not already being pinned to a
-        specific value (e.g. because it is selected by another symbol).
-
-        For strings and numbers, this corresponds to just being visible. (See
-        Symbol.get_visibility().)"""
-        if self.is_special_:
-            return False
-        if self.type == BOOL or self.type == TRISTATE:
-            rev_dep = self.config._eval_expr(self.rev_dep)
-            # A bool selected to "m" gets promoted to "y", pinning it
-            if rev_dep == "m" and self.type == BOOL:
-                return False
-            return TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]
-        return _get_visibility(self) != "n"
-
-    def is_defined(self):
-        """Returns False if the symbol is referred to in the Kconfig but never
-        actually defined."""
-        return self.is_defined_
-
-    def is_special(self):
-        """Returns True if the symbol is one of the special symbols n, m, y, or
-        UNAME_RELEASE, or gets its value from the environment."""
-        return self.is_special_
-
-    def is_from_environment(self):
-        """Returns True if the symbol gets its value from the environment."""
-        return self.is_from_env
-
-    def has_ranges(self):
-        """Returns True if the symbol is of type INT or HEX and has ranges that
-        limit what values it can take on."""
-        return bool(self.ranges)
-
-    def is_choice_symbol(self):
-        """Returns True if the symbol is in a choice statement and is an actual
-        choice symbol (see Choice.get_symbols())."""
-        return self.is_choice_sym
-
-    def is_choice_selection(self):
-        """Returns True if the symbol is contained in a choice statement and is
-        the selected item. Equivalent to
-
-        sym.is_choice_symbol() and sym.get_parent().get_selection() is sym"""
-        return self.is_choice_sym and self.parent.get_selection() is self
-
-    def is_allnoconfig_y(self):
-        """Returns True if the symbol has the 'allnoconfig_y' option set."""
-        return self.allnoconfig_y
-
-    def __str__(self):
-        """Returns a string containing various information about the symbol."""
-        return self.config._get_sym_or_choice_str(self)
-
-    #
-    # Private methods
-    #
-
-    def __init__(self):
-        """Symbol constructor -- not intended to be called directly by
-        Kconfiglib clients."""
-
-        self.name = None
-        self.type = UNKNOWN
-        self.prompts = []
-        self.def_exprs = [] # 'default' properties
-        self.ranges = [] # 'range' properties (for int and hex)
-        self.help = None # Help text
-        self.rev_dep = "n" # Reverse (select-related) dependencies
-        self.weak_rev_dep = "n" # Weak reverse (imply-related) dependencies
-        self.config = None
-        self.parent = None
-
-        self.user_val = None # Value set by user
-
-        # The prompt, default value, select, and imply conditions without any
-        # dependencies from menus and ifs propagated to them
-        self.orig_prompts = []
-        self.orig_def_exprs = []
-        self.orig_selects = []
-        self.orig_implies = []
-
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this symbol (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # The set of symbols selected by this symbol (see
-        # get_selected_symbols())
-        self.selected_syms = set()
-        # The set of symbols implied by this symbol (see get_implied_symbols())
-        self.implied_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = set()
-
-        # This records only dependencies from enclosing ifs and menus together
-        # with local 'depends on' dependencies. Needed when determining actual
-        # choice items (hrrrr...). See Choice._determine_actual_symbols().
-        self.menu_dep = None
-
-        # See Symbol.get_ref/def_locations().
-        self.def_locations = []
-        self.ref_locations = []
-
-        # Populated in Config._build_dep() after parsing. Links the symbol to
-        # the symbols that immediately depend on it (in a caching/invalidation
-        # sense). The total set of dependent symbols for the symbol (the
-        # transitive closure) is calculated on an as-needed basis in
-        # _get_dependent().
-        self.dep = set()
-
-        # Cached values
-
-        # Caches the calculated value
-        self.cached_val = None
-        # Caches the visibility, which acts as an upper bound on the value
-        self.cached_visibility = None
-        # Caches the total list of dependent symbols. Calculated in
-        # _get_dependent().
-        self.cached_deps = None
-
-        # Flags
-
-        # Does the symbol have an entry in the Kconfig file? The trailing
-        # underscore avoids a collision with is_defined().
-        self.is_defined_ = False
-        # Should the symbol get an entry in .config?
-        self.write_to_conf = False
-        # Set to true when _make_conf() is called on a symbol, so that symbols
-        # defined in multiple locations only get one .config entry. We need to
-        # reset it prior to writing out a new .config.
-        self.already_written = False
-        # This is set to True for "actual" choice symbols; see
-        # Choice._determine_actual_symbols().
-        self.is_choice_sym = False
-        # Does the symbol get its value in some special way, e.g. from the
-        # environment or by being one of the special symbols n, m, and y? If
-        # so, the value is stored in self.cached_val, which is never
-        # invalidated. The trailing underscore avoids a collision with
-        # is_special().
-        self.is_special_ = False
-        # Does the symbol get its value from the environment?
-        self.is_from_env = False
-        # Does the symbol have the 'allnoconfig_y' option set?
-        self.allnoconfig_y = False
-
-    def _invalidate(self):
-        if self.is_special_:
-            return
-
-        if self.is_choice_sym:
-            self.parent._invalidate()
-
-        self.cached_val = None
-        self.cached_visibility = None
-
-    def _invalidate_dependent(self):
-        for sym in self._get_dependent():
-            sym._invalidate()
-
-    def _set_user_value_no_invalidate(self, v, suppress_load_warnings):
-        """Like set_user_value(), but does not invalidate any symbols.
-
-        suppress_load_warnings: some warnings are annoying when loading a
-           .config that can be helpful when manually invoking set_user_value().
-           This flag is set to True to suppress such warnings.
-
-           Perhaps this could be made optional for load_config() instead."""
-
-        if self.is_special_:
-            if self.is_from_env:
-                self.config._warn('attempt to assign the value "{0}" to the '
-                                  'symbol {1}, which gets its value from the '
-                                  'environment. Assignment ignored.'
-                                  .format(v, self.name))
-            else:
-                self.config._warn('attempt to assign the value "{0}" to the '
-                                  'special symbol {1}. Assignment ignored.'
-                                  .format(v, self.name))
-            return
-
-        if not self.is_defined_:
-            filename, linenr = self.ref_locations[0]
-            if self.config.print_undef_assign:
-                _stderr_msg('note: attempt to assign the value "{0}" to {1}, '
-                            "which is referenced at {2}:{3} but never "
-                            "defined. Assignment ignored."
-                            .format(v, self.name, filename, linenr))
-            return
+        # If the new user value matches the old, nothing changes, and we can
+        # avoid invalidating cached values.
+        #
+        # This optimization is skipped for choice symbols: Setting a choice
+        # symbol's user value to y might change the state of the choice, so it
+        # wouldn't be safe (symbol user values always match the values set in a
+        # .config file or via set_value(), and are never implicitly updated).
+        if value == self.user_value and not self.choice:
+            self._was_set = True
+            return True
 
         # Check if the value is valid for our type
-        if not ((self.type == BOOL     and (v == "y" or v == "n")   ) or
-                (self.type == TRISTATE and (v == "y" or v == "m" or
-                                            v == "n")               ) or
-                (self.type == STRING                                ) or
-                (self.type == INT      and _is_base_n(v, 10)        ) or
-                (self.type == HEX      and _is_base_n(v, 16)        )):
-            self.config._warn('the value "{0}" is invalid for {1}, which has '
-                              "type {2}. Assignment ignored."
-                              .format(v, self.name, TYPENAME[self.type]))
-            return
+        if not (self.orig_type is BOOL     and value in (2, 0)     or
+                self.orig_type is TRISTATE and value in TRI_TO_STR or
+                value.__class__ is str and
+                (self.orig_type is STRING                        or
+                 self.orig_type is INT and _is_base_n(value, 10) or
+                 self.orig_type is HEX and _is_base_n(value, 16)
+                                       and int(value, 16) >= 0)):
 
-        if not self.prompts and not suppress_load_warnings:
-            self.config._warn('assigning "{0}" to the symbol {1} which '
-                              'lacks prompts and thus has visibility "n". '
-                              'The assignment will have no effect.'
-                              .format(v, self.name))
+            # Display tristate values as n, m, y in the warning
+            self.kconfig._warn(
+                "the value {} is invalid for {}, which has type {} -- "
+                "assignment ignored"
+                .format(TRI_TO_STR[value] if value in TRI_TO_STR else
+                            "'{}'".format(value),
+                        _name_and_loc(self), TYPE_TO_STR[self.orig_type]))
 
-        self.user_val = v
+            return False
 
-        if self.is_choice_sym and (self.type == BOOL or self.type == TRISTATE):
-            choice = self.parent
-            if v == "y":
-                choice.user_val = self
-                choice.user_mode = "y"
-            elif v == "m":
-                choice.user_val = None
-                choice.user_mode = "m"
-
-    def _unset_user_value_no_recursive_invalidate(self):
-        self._invalidate()
-        self.user_val = None
-
-        if self.is_choice_sym:
-            self.parent._unset_user_value()
-
-    def _make_conf(self, append_fn):
-        if self.already_written:
-            return
-
-        self.already_written = True
-
-        # Note: write_to_conf is determined in get_value()
-        val = self.get_value()
-        if not self.write_to_conf:
-            return
-
-        if self.type == BOOL or self.type == TRISTATE:
-            append_fn("{0}{1}={2}".format(self.config.config_prefix, self.name, val)
-                      if val == "y" or val == "m" else
-                      "# {0}{1} is not set".format(self.config.config_prefix, self.name))
-
-        elif self.type == INT or self.type == HEX:
-            append_fn("{0}{1}={2}".format(self.config.config_prefix, self.name, val))
-
-        elif self.type == STRING:
-            # Escape \ and "
-            append_fn('{0}{1}="{2}"'
-                      .format(self.config.config_prefix, self.name,
-                              val.replace("\\", "\\\\").replace('"', '\\"')))
+        self.user_value = value
+        self._was_set = True
 
+        if self.choice and value == 2:
+            # Setting a choice symbol to y makes it the user selection of the
+            # choice. Like for symbol user values, the user selection is not
+            # guaranteed to match the actual selection of the choice, as
+            # dependencies come into play.
+            self.choice.user_selection = self
+            self.choice._was_set = True
+            self.choice._rec_invalidate()
         else:
-            _internal_error("Internal error while creating .config: unknown "
-                            'type "{0}".'.format(self.type))
+            self._rec_invalidate_if_has_prompt()
 
-    def _get_dependent(self):
-        """Returns the set of symbols that should be invalidated if the value
-        of the symbol changes, because they might be affected by the change.
-        Note that this is an internal API -- it's probably of limited
-        usefulness to clients."""
-        if self.cached_deps is not None:
-            return self.cached_deps
+        return True
 
-        res = set(self.dep)
-        for s in self.dep:
-            res |= s._get_dependent()
+    def unset_value(self):
+        """
+        Removes any user value from the symbol, as if the symbol had never
+        gotten a user value via Kconfig.load_config() or Symbol.set_value().
+        """
+        if self.user_value is not None:
+            self.user_value = None
+            self._rec_invalidate_if_has_prompt()
 
-        if self.is_choice_sym:
-            # Choice symbols also depend (recursively) on their siblings. The
-            # siblings are not included in 'dep' to avoid dependency loops.
-            for sibling in self.parent.actual_symbols:
-                if sibling is not self:
-                    res.add(sibling)
-                    res |= sibling.dep
-                    for s in sibling.dep:
-                        res |= s._get_dependent()
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        return {item for node in self.nodes for item in node.referenced}
 
-        self.cached_deps = res
-        return res
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [d for node in self.nodes for d in node.orig_defaults]
 
-    def _has_auto_menu_dep_on(self, on):
-        """See Choice._determine_actual_symbols()."""
-        if not isinstance(self.parent, Choice):
-            _internal_error("Attempt to determine auto menu dependency for "
-                            "symbol ouside of choice.")
+    @property
+    def orig_selects(self):
+        """
+        See the class documentation.
+        """
+        return [s for node in self.nodes for s in node.orig_selects]
 
-        if not self.prompts:
-            # If we have no prompt, use the menu dependencies instead (what was
-            # specified with 'depends on')
-            return self.menu_dep is not None and \
-                   self.config._expr_depends_on(self.menu_dep, on)
+    @property
+    def orig_implies(self):
+        """
+        See the class documentation.
+        """
+        return [i for node in self.nodes for i in node.orig_implies]
 
-        for _, cond_expr in self.prompts:
-            if self.config._expr_depends_on(cond_expr, on):
-                return True
+    @property
+    def orig_ranges(self):
+        """
+        See the class documentation.
+        """
+        return [r for node in self.nodes for r in node.orig_ranges]
 
-        return False
+    def __repr__(self):
+        """
+        Returns a string with information about the symbol (including its name,
+        value, visibility, and location(s)) when it is evaluated on e.g. the
+        interactive Python prompt.
+        """
+        fields = ["symbol " + self.name, TYPE_TO_STR[self.type]]
+        add = fields.append
 
-class Menu(Item):
+        for node in self.nodes:
+            if node.prompt:
+                add('"{}"'.format(node.prompt[0]))
 
-    """Represents a menu statement."""
+        # Only add quotes for non-bool/tristate symbols
+        add("value " + (self.str_value if self.orig_type in _BOOL_TRISTATE
+                        else '"{}"'.format(self.str_value)))
 
-    #
-    # Public interface
-    #
+        if not self.is_constant:
+            # These aren't helpful to show for constant symbols
 
-    def get_config(self):
-        """Return the Config instance this menu is from."""
-        return self.config
+            if self.user_value is not None:
+                # Only add quotes for non-bool/tristate symbols
+                add("user value " + (TRI_TO_STR[self.user_value]
+                                     if self.orig_type in _BOOL_TRISTATE
+                                     else '"{}"'.format(self.user_value)))
 
-    def get_title(self):
-        """Returns the title text of the menu."""
-        return self.title
+            add("visibility " + TRI_TO_STR[self.visibility])
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the menu, or
-        None if the menu is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
+            if self.choice:
+                add("choice symbol")
 
-    def get_location(self):
-        """Returns the location of the menu as a (filename, linenr) tuple,
-        where filename is a string and linenr an int."""
-        return (self.filename, self.linenr)
+            if self.is_allnoconfig_y:
+                add("allnoconfig_y")
 
-    def get_items(self, recursive=False):
-        """Returns a list containing the items (symbols, menus, choice
-        statements and comments) in in the menu, in the same order that the
-        items appear within the menu.
+            if self is self.kconfig.defconfig_list:
+                add("is the defconfig_list symbol")
 
-        recursive (default: False): True if items contained in items within the
-           menu should be included recursively (preorder)."""
+            if self.env_var is not None:
+                add("from environment variable " + self.env_var)
 
-        if not recursive:
-            return self.block
+            if self is self.kconfig.modules:
+                add("is the modules symbol")
 
-        res = []
-        for item in self.block:
-            res.append(item)
-            if isinstance(item, Menu):
-                res.extend(item.get_items(True))
-            elif isinstance(item, Choice):
-                res.extend(item.get_items())
-        return res
+            add("direct deps " + TRI_TO_STR[expr_value(self.direct_dep)])
 
-    def get_symbols(self, recursive=False):
-        """Returns a list containing the symbols in the menu, in the same order
-        that they appear within the menu.
+        if self.nodes:
+            for node in self.nodes:
+                add("{}:{}".format(node.filename, node.linenr))
+        else:
+            add("constant" if self.is_constant else "undefined")
 
-        recursive (default: False): True if symbols contained in items within
-           the menu should be included recursively."""
-
-        return [item for item in self.get_items(recursive) if
-                isinstance(item, Symbol)]
-
-    def get_visibility(self):
-        """Returns the visibility of the menu. This also affects the visibility
-        of subitems. See also Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
-
-    def get_visible_if_visibility(self):
-        """Returns the visibility the menu gets from its 'visible if'
-        condition. "y" if the menu has no 'visible if' condition."""
-        return self.config._eval_expr(self.visible_if_expr)
-
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
+        return "<{}>".format(", ".join(fields))
 
     def __str__(self):
-        """Returns a string containing various information about the menu."""
-        depends_on_str = self.config._expr_val_str(self.orig_deps,
-                                                   "(no dependencies)")
-        visible_if_str = self.config._expr_val_str(self.visible_if_expr,
-                                                   "(no dependencies)")
+        """
+        Returns a string representation of the symbol when it is printed.
+        Matches the Kconfig format, with any parent dependencies propagated to
+        the 'depends on' condition.
 
-        additional_deps_str = " " + \
-          self.config._expr_val_str(self.deps_from_containing,
-                                    "(no additional dependencies)")
+        The string is constructed by joining the strings returned by
+        MenuNode.__str__() for each of the symbol's menu nodes, so symbols
+        defined in multiple locations will return a string with all
+        definitions.
 
-        return _lines("Menu",
-                      "Title                     : " + self.title,
-                      "'depends on' dependencies : " + depends_on_str,
-                      "'visible if' dependencies : " + visible_if_str,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Location: {0}:{1}".format(self.filename, self.linenr))
+        The returned string does not end in a newline. An empty string is
+        returned for undefined and constant symbols.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like Symbol.__str__(), but allows a custom format to be used for
+        all symbol/choice references. See expr_str().
+        """
+        return "\n\n".join(node.custom_str(sc_expr_str_fn)
+                           for node in self.nodes)
 
     #
     # Private methods
     #
 
     def __init__(self):
-        """Menu constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+        """
+        Symbol constructor -- not intended to be called directly by Kconfiglib
+        clients.
+        """
+        # These attributes are always set on the instance from outside and
+        # don't need defaults:
+        #   kconfig
+        #   direct_dep
+        #   is_constant
+        #   name
+        #   rev_dep
+        #   weak_rev_dep
 
-        self.title = None
-        self.dep_expr = None
-        self.visible_if_expr = None
-        self.block = [] # List of contained items
-        self.config = None
-        self.parent = None
+        # - UNKNOWN == 0
+        # - _visited is used during tree iteration and dep. loop detection
+        self.orig_type = self._visited = 0
 
-        # Dependency expression without dependencies from enclosing menus and
-        # ifs propagated
-        self.orig_deps = None
+        self.nodes = []
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this menu (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = None
+        self.defaults = []
+        self.selects = []
+        self.implies = []
+        self.ranges = []
 
-        self.filename = None
-        self.linenr = None
+        self.user_value = \
+        self.choice = \
+        self.env_var = \
+        self._cached_str_val = self._cached_tri_val = self._cached_vis = \
+        self._cached_assignable = None
 
-    def _make_conf(self, append_fn):
-        if self.config._eval_expr(self.dep_expr) != "n" and \
-           self.config._eval_expr(self.visible_if_expr) != "n":
-            append_fn("\n#\n# {0}\n#".format(self.title))
-        _make_block_conf(self.block, append_fn)
+        # _write_to_conf is calculated along with the value. If True, the
+        # Symbol gets a .config entry.
 
-class Choice(Item):
+        self.is_allnoconfig_y = \
+        self._was_set = \
+        self._write_to_conf = False
 
-    """Represents a choice statement. A choice can be in one of three modes:
+        # See Kconfig._build_dep()
+        self._dependents = set()
 
-    "n" - The choice is not visible and no symbols can be selected.
+    def _assignable(self):
+        # Worker function for the 'assignable' attribute
 
-    "m" - Any number of symbols can be set to "m". The rest will be "n". This
-          is safe since potentially conflicting options don't actually get
-          compiled into the kernel simultaneously with "m".
+        if self.orig_type not in _BOOL_TRISTATE:
+            return ()
 
-    "y" - One symbol will be "y" while the rest are "n".
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+        if not vis:
+            return ()
 
-    Only tristate choices can be in "m" mode, and the visibility of the choice
-    is an upper bound on the mode, so that e.g. a choice that depends on a
-    symbol with value "m" will be in "m" mode.
+        rev_dep_val = expr_value(self.rev_dep)
 
-    The mode changes automatically when a value is assigned to a symbol within
-    the choice.
+        if vis == 2:
+            if self.choice:
+                return (2,)
 
-    See Symbol.get_visibility() too."""
+            if not rev_dep_val:
+                if self.type is BOOL or expr_value(self.weak_rev_dep) == 2:
+                    return (0, 2)
+                return (0, 1, 2)
 
-    #
-    # Public interface
-    #
+            if rev_dep_val == 2:
+                return (2,)
 
-    def get_config(self):
-        """Returns the Config instance this choice is from."""
-        return self.config
+            # rev_dep_val == 1
 
-    def get_name(self):
-        """For named choices, returns the name. Returns None for unnamed
-        choices. No named choices appear anywhere in the kernel Kconfig files
-        as of Linux 3.7.0-rc8."""
-        return self.name
+            if self.type is BOOL or expr_value(self.weak_rev_dep) == 2:
+                return (2,)
+            return (1, 2)
 
-    def get_type(self):
-        """Returns the type of the choice. See Symbol.get_type()."""
-        return self.type
+        # vis == 1
 
-    def get_prompts(self):
-        """Returns a list of prompts defined for the choice, in the order they
-        appear in the configuration files. Returns the empty list for choices
-        with no prompt.
+        # Must be a tristate here, because bool m visibility gets promoted to y
 
-        This list will have a single entry for the vast majority of choices
-        having prompts, but having multiple prompts for a single choice is
-        possible through having multiple 'choice' entries for it (though I'm
-        not sure if that ever happens in practice)."""
-        return [prompt for prompt, _ in self.orig_prompts]
+        if not rev_dep_val:
+            return (0, 1) if expr_value(self.weak_rev_dep) != 2 else (0, 2)
 
-    def get_help(self):
-        """Returns the help text of the choice, or None if the choice has no
-        help text."""
-        return self.help
+        if rev_dep_val == 2:
+            return (2,)
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the choice, or
-        None if the choice is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
+        # vis == rev_dep_val == 1
 
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the choice is defined. For
-        the vast majority of choices (all of them as of Linux 3.7.0-rc8) this
-        list will only contain one element, but its possible for named choices
-        to be defined in multiple locations."""
-        return self.def_locations
-
-    def get_selection(self):
-        """Returns the symbol selected (either by the user or through
-        defaults), or None if either no symbol is selected or the mode is not
-        "y"."""
-        if self.cached_selection is not None:
-            if self.cached_selection == NO_SELECTION:
-                return None
-            return self.cached_selection
-
-        if self.get_mode() != "y":
-            return self._cache_ret(None)
-
-        # User choice available?
-        if self.user_val is not None and _get_visibility(self.user_val) == "y":
-            return self._cache_ret(self.user_val)
-
-        if self.optional:
-            return self._cache_ret(None)
-
-        return self._cache_ret(self.get_selection_from_defaults())
-
-    def get_selection_from_defaults(self):
-        """Like Choice.get_selection(), but acts as if no symbol has been
-        selected by the user and no 'optional' flag is in effect."""
-
-        if not self.actual_symbols:
-            return None
-
-        for symbol, cond_expr in self.def_exprs:
-            if self.config._eval_expr(cond_expr) != "n":
-                chosen_symbol = symbol
-                break
-        else:
-            chosen_symbol = self.actual_symbols[0]
-
-        # Is the chosen symbol visible?
-        if _get_visibility(chosen_symbol) != "n":
-            return chosen_symbol
-        # Otherwise, pick the first visible symbol
-        for sym in self.actual_symbols:
-            if _get_visibility(sym) != "n":
-                return sym
-        return None
-
-    def get_user_selection(self):
-        """If the choice is in "y" mode and has a user-selected symbol, returns
-        that symbol. Otherwise, returns None."""
-        return self.user_val
-
-    def get_items(self):
-        """Gets all items contained in the choice in the same order as within
-        the configuration ("items" instead of "symbols" since choices and
-        comments might appear within choices. This only happens in one place as
-        of Linux 3.7.0-rc8, in drivers/usb/gadget/Kconfig)."""
-        return self.block
-
-    def get_symbols(self):
-        """Returns a list containing the choice's symbols.
-
-        A quirk (perhaps a bug) of Kconfig is that you can put items within a
-        choice that will not be considered members of the choice insofar as
-        selection is concerned. This happens for example if one symbol within a
-        choice 'depends on' the symbol preceding it, or if you put non-symbol
-        items within choices.
-
-        As of Linux 3.7.0-rc8, this seems to be used intentionally in one
-        place: drivers/usb/gadget/Kconfig.
-
-        This function returns the "proper" symbols of the choice in the order
-        they appear in the choice, excluding such items. If you want all items
-        in the choice, use get_items()."""
-        return self.actual_symbols
-
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
-
-    def get_visibility(self):
-        """Returns the visibility of the choice statement: one of "n", "m" or
-        "y". This acts as an upper limit on the mode of the choice (though bool
-        choices can only have the mode "y"). See the class documentation for an
-        explanation of modes."""
-        return _get_visibility(self)
-
-    def get_mode(self):
-        """Returns the mode of the choice. See the class documentation for
-        an explanation of modes."""
-        minimum_mode = "n" if self.optional else "m"
-        mode = self.user_mode if self.user_mode is not None else minimum_mode
-        mode = self.config._eval_min(mode, _get_visibility(self))
-
-        # Promote "m" to "y" for boolean choices
-        if mode == "m" and self.type == BOOL:
-            return "y"
-
-        return mode
-
-    def is_optional(self):
-        """Returns True if the choice has the 'optional' flag set (and so will
-        default to "n" mode)."""
-        return self.optional
-
-    def __str__(self):
-        """Returns a string containing various information about the choice
-        statement."""
-        return self.config._get_sym_or_choice_str(self)
-
-    #
-    # Private methods
-    #
-
-    def __init__(self):
-        """Choice constructor -- not intended to be called directly by
-        Kconfiglib clients."""
-
-        self.name = None # Yes, choices can be named
-        self.type = UNKNOWN
-        self.prompts = []
-        self.def_exprs = [] # 'default' properties
-        self.help = None # Help text
-        self.block = [] # List of contained items
-        self.config = None
-        self.parent = None
-
-        self.user_val = None
-        self.user_mode = None
-
-        # We need to filter out symbols that appear within the choice block but
-        # are not considered choice items (see
-        # Choice._determine_actual_symbols()) This list holds the "actual"
-        # choice items.
-        self.actual_symbols = []
-
-        # The prompts and default values without any dependencies from
-        # enclosing menus and ifs propagated
-        self.orig_prompts = []
-        self.orig_def_exprs = []
-
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this choice (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = set()
-
-        # See Choice.get_def_locations()
-        self.def_locations = []
-
-        # Cached values
-        self.cached_selection = None
-        self.cached_visibility = None
-
-        self.optional = False
-
-    def _determine_actual_symbols(self):
-        """If a symbol's visibility depends on the preceding symbol within a
-        choice, it is no longer viewed as a choice item. (This is quite
-        possibly a bug, but some things consciously use it... ugh. It stems
-        from automatic submenu creation.) In addition, it's possible to have
-        choices and comments within choices, and those shouldn't be considered
-        choice items either. Only drivers/usb/gadget/Kconfig seems to depend on
-        any of this. This method computes the "actual" items in the choice and
-        sets the is_choice_sym flag on them (retrieved via is_choice_symbol()).
-
-        Don't let this scare you: an earlier version simply checked for a
-        sequence of symbols where all symbols after the first appeared in the
-        'depends on' expression of the first, and that worked fine.  The added
-        complexity is to be future-proof in the event that
-        drivers/usb/gadget/Kconfig turns even more sinister. It might very well
-        be overkilling things (especially if that file is refactored ;)."""
-
-        # Items might depend on each other in a tree structure, so we need a
-        # stack to keep track of the current tentative parent
-        stack = []
-
-        for item in self.block:
-            if not isinstance(item, Symbol):
-                stack = []
-                continue
-
-            while stack:
-                if item._has_auto_menu_dep_on(stack[-1]):
-                    # The item should not be viewed as a choice item, so don't
-                    # set item.is_choice_sym
-                    stack.append(item)
-                    break
-                else:
-                    stack.pop()
-            else:
-                item.is_choice_sym = True
-                self.actual_symbols.append(item)
-                stack.append(item)
-
-    def _cache_ret(self, selection):
-        # As None is used to indicate the lack of a cached value we can't use
-        # that to cache the fact that the choice has no selection. Instead, we
-        # use the symbolic constant NO_SELECTION.
-        if selection is None:
-            self.cached_selection = NO_SELECTION
-        else:
-            self.cached_selection = selection
-
-        return selection
+        return (1,)
 
     def _invalidate(self):
-        self.cached_selection = None
-        self.cached_visibility = None
+        # Marks the symbol as needing to be recalculated
 
-    def _unset_user_value(self):
-        self._invalidate()
-        self.user_val = None
-        self.user_mode = None
+        self._cached_str_val = self._cached_tri_val = self._cached_vis = \
+        self._cached_assignable = None
 
-    def _make_conf(self, append_fn):
-        _make_block_conf(self.block, append_fn)
+    def _rec_invalidate(self):
+        # Invalidates the symbol and all items that (possibly) depend on it
 
-class Comment(Item):
+        if self is self.kconfig.modules:
+            # Invalidating MODULES has wide-ranging effects
+            self.kconfig._invalidate_all()
+        else:
+            self._invalidate()
 
-    """Represents a comment statement."""
+            for item in self._dependents:
+                # _cached_vis doubles as a flag that tells us whether 'item'
+                # has cached values, because it's calculated as a side effect
+                # of calculating all other (non-constant) cached values.
+                #
+                # If item._cached_vis is None, it means there can't be cached
+                # values on other items that depend on 'item', because if there
+                # were, some value on 'item' would have been calculated and
+                # item._cached_vis set as a side effect. It's therefore safe to
+                # stop the invalidation at symbols with _cached_vis None.
+                #
+                # This approach massively speeds up scripts that set a lot of
+                # values, vs simply invalidating all possibly dependent symbols
+                # (even when you already have a list of all the dependent
+                # symbols, because some symbols get huge dependency trees).
+                #
+                # This gracefully handles dependency loops too, which is nice
+                # for choices, where the choice depends on the choice symbols
+                # and vice versa.
+                if item._cached_vis is not None:
+                    item._rec_invalidate()
+
+    def _rec_invalidate_if_has_prompt(self):
+        # Invalidates the symbol and its dependent symbols, but only if the
+        # symbol has a prompt. User values never have an effect on promptless
+        # symbols, so we skip invalidation for them as an optimization.
+        #
+        # This also prevents constant (quoted) symbols from being invalidated
+        # if set_value() is called on them, which would make them lose their
+        # value and break things.
+        #
+        # Prints a warning if the symbol has no prompt. In some contexts (e.g.
+        # when loading a .config files) assignments to promptless symbols are
+        # normal and expected, so the warning can be disabled.
+
+        for node in self.nodes:
+            if node.prompt:
+                self._rec_invalidate()
+                return
+
+        if self.kconfig._warn_assign_no_prompt:
+            self.kconfig._warn(_name_and_loc(self) + " has no prompt, meaning "
+                               "user values have no effect on it")
+
+    def _str_default(self):
+        # write_min_config() helper function. Returns the value the symbol
+        # would get from defaults if it didn't have a user value. Uses exactly
+        # the same algorithm as the C implementation (though a bit cleaned up),
+        # for compatibility.
+
+        if self.orig_type in _BOOL_TRISTATE:
+            val = 0
+
+            # Defaults, selects, and implies do not affect choice symbols
+            if not self.choice:
+                for default, cond in self.defaults:
+                    cond_val = expr_value(cond)
+                    if cond_val:
+                        val = min(expr_value(default), cond_val)
+                        break
+
+                val = max(expr_value(self.rev_dep),
+                          expr_value(self.weak_rev_dep),
+                          val)
+
+                # Transpose mod to yes if type is bool (possibly due to modules
+                # being disabled)
+                if val == 1 and self.type is BOOL:
+                    val = 2
+
+            return TRI_TO_STR[val]
+
+        if self.orig_type:  # STRING/INT/HEX
+            for default, cond in self.defaults:
+                if expr_value(cond):
+                    return default.str_value
+
+        return ""
+
+    def _warn_select_unsatisfied_deps(self):
+        # Helper for printing an informative warning when a symbol with
+        # unsatisfied direct dependencies (dependencies from 'depends on', ifs,
+        # and menus) is selected by some other symbol. Also warn if a symbol
+        # whose direct dependencies evaluate to m is selected to y.
+
+        msg = "{} has direct dependencies {} with value {}, but is " \
+              "currently being {}-selected by the following symbols:" \
+              .format(_name_and_loc(self), expr_str(self.direct_dep),
+                      TRI_TO_STR[expr_value(self.direct_dep)],
+                      TRI_TO_STR[expr_value(self.rev_dep)])
+
+        # The reverse dependencies from each select are ORed together
+        for select in split_expr(self.rev_dep, OR):
+            if expr_value(select) <= expr_value(self.direct_dep):
+                # Only include selects that exceed the direct dependencies
+                continue
+
+            # - 'select A if B' turns into A && B
+            # - 'select A' just turns into A
+            #
+            # In both cases, we can split on AND and pick the first operand
+            selecting_sym = split_expr(select, AND)[0]
+
+            msg += "\n - {}, with value {}, direct dependencies {} " \
+                   "(value: {})" \
+                   .format(_name_and_loc(selecting_sym),
+                           selecting_sym.str_value,
+                           expr_str(selecting_sym.direct_dep),
+                           TRI_TO_STR[expr_value(selecting_sym.direct_dep)])
+
+            if select.__class__ is tuple:
+                msg += ", and select condition {} (value: {})" \
+                       .format(expr_str(select[2]),
+                               TRI_TO_STR[expr_value(select[2])])
+
+        self.kconfig._warn(msg)
+
+
+class Choice(object):
+    """
+    Represents a choice statement:
+
+      choice
+          ...
+      endchoice
+
+    The following attributes are available on Choice instances. They should be
+    treated as read-only, and some are implemented through @property magic (but
+    are still efficient to access due to internal caching).
+
+    Note: Prompts, help texts, and locations are stored in the Choice's
+    MenuNode(s) rather than in the Choice itself. Check the MenuNode class and
+    the Choice.nodes attribute. This organization matches the C tools.
+
+    name:
+      The name of the choice, e.g. "FOO" for 'choice FOO', or None if the
+      Choice has no name.
+
+    type:
+      The type of the choice. One of BOOL, TRISTATE, UNKNOWN. UNKNOWN is for
+      choices defined without a type where none of the contained symbols have a
+      type either (otherwise the choice inherits the type of the first symbol
+      defined with a type).
+
+      When running without modules (CONFIG_MODULES=n), TRISTATE choices
+      magically change type to BOOL. This matches the C tools, and makes sense
+      for menuconfig-like functionality.
+
+    orig_type:
+      The type as given in the Kconfig file, without any magic applied. Used
+      when printing the choice.
+
+    tri_value:
+      The tristate value (mode) of the choice. A choice can be in one of three
+      modes:
+
+        0 (n) - The choice is disabled and no symbols can be selected. For
+                visible choices, this mode is only possible for choices with
+                the 'optional' flag set (see kconfig-language.txt).
+
+        1 (m) - Any number of choice symbols can be set to m, the rest will
+                be n.
+
+        2 (y) - One symbol will be y, the rest n.
+
+      Only tristate choices can be in m mode. The visibility of the choice is
+      an upper bound on the mode, and the mode in turn is an upper bound on the
+      visibility of the choice symbols.
+
+      To change the mode, use Choice.set_value().
+
+      Implementation note:
+        The C tools internally represent choices as a type of symbol, with
+        special-casing in many code paths. This is why there is a lot of
+        similarity to Symbol. The value (mode) of a choice is really just a
+        normal symbol value, and an implicit reverse dependency forces its
+        lower bound to m for visible non-optional choices (the reverse
+        dependency is 'm && <visibility>').
+
+        Symbols within choices get the choice propagated as a dependency to
+        their properties. This turns the mode of the choice into an upper bound
+        on e.g. the visibility of choice symbols, and explains the gotcha
+        related to printing choice symbols mentioned in the module docstring.
+
+        Kconfiglib uses a separate Choice class only because it makes the code
+        and interface less confusing (especially in a user-facing interface).
+        Corresponding attributes have the same name in the Symbol and Choice
+        classes, for consistency and compatibility.
+
+    assignable:
+      See the symbol class documentation. Gives the assignable values (modes).
+
+    visibility:
+      See the Symbol class documentation. Acts on the value (mode).
+
+    selection:
+      The Symbol instance of the currently selected symbol. None if the Choice
+      is not in y mode or has no selected symbol (due to unsatisfied
+      dependencies on choice symbols).
+
+      WARNING: Do not assign directly to this. It will break things. Call
+      sym.set_value(2) on the choice symbol you want to select instead.
+
+    user_value:
+      The value (mode) selected by the user through Choice.set_value(). Either
+      0, 1, or 2, or None if the user hasn't selected a mode. See
+      Symbol.user_value.
+
+      WARNING: Do not assign directly to this. It will break things. Use
+      Choice.set_value() instead.
+
+    user_selection:
+      The symbol selected by the user (by setting it to y). Ignored if the
+      choice is not in y mode, but still remembered so that the choice "snaps
+      back" to the user selection if the mode is changed back to y. This might
+      differ from 'selection' due to unsatisfied dependencies.
+
+      WARNING: Do not assign directly to this. It will break things. Call
+      sym.set_value(2) on the choice symbol to be selected instead.
+
+    syms:
+      List of symbols contained in the choice.
+
+      Obscure gotcha: If a symbol depends on the previous symbol within a
+      choice so that an implicit menu is created, it won't be a choice symbol,
+      and won't be included in 'syms'.
+
+    nodes:
+      A list of MenuNodes for this choice. In practice, the list will probably
+      always contain a single MenuNode, but it is possible to give a choice a
+      name and define it in multiple locations.
+
+    defaults:
+      List of (symbol, cond) tuples for the choice's 'defaults' properties. For
+      example, 'default A if B && C' is represented as (A, (AND, B, C)). If
+      there is no condition, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to
+      'default' conditions.
+
+    orig_defaults:
+      See the corresponding attribute on the MenuNode class.
+
+    direct_dep:
+      See Symbol.direct_dep.
+
+    referenced:
+      A set() with all symbols referenced in the properties and property
+      conditions of the choice.
+
+      Also includes dependencies from surrounding menus and ifs, because those
+      get propagated to the choice (see the 'Intro to symbol values' section in
+      the module docstring).
+
+    is_optional:
+      True if the choice has the 'optional' flag set on it and can be in
+      n mode.
+
+    kconfig:
+      The Kconfig instance this choice is from.
+    """
+    __slots__ = (
+        "_cached_assignable",
+        "_cached_selection",
+        "_cached_vis",
+        "_dependents",
+        "_visited",
+        "_was_set",
+        "defaults",
+        "direct_dep",
+        "is_constant",
+        "is_optional",
+        "kconfig",
+        "name",
+        "nodes",
+        "orig_type",
+        "syms",
+        "user_selection",
+        "user_value",
+    )
 
     #
     # Public interface
     #
 
-    def get_config(self):
-        """Returns the Config instance this comment is from."""
-        return self.config
+    @property
+    def type(self):
+        """
+        Returns the type of the choice. See Symbol.type.
+        """
+        if self.orig_type is TRISTATE and not self.kconfig.modules.tri_value:
+            return BOOL
+        return self.orig_type
 
-    def get_text(self):
-        """Returns the text of the comment."""
-        return self.text
+    @property
+    def str_value(self):
+        """
+        See the class documentation.
+        """
+        return TRI_TO_STR[self.tri_value]
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the comment, or
-        None if the comment is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
+    @property
+    def tri_value(self):
+        """
+        See the class documentation.
+        """
+        # This emulates a reverse dependency of 'm && visibility' for
+        # non-optional choices, which is how the C implementation does it
 
-    def get_location(self):
-        """Returns the location of the comment as a (filename, linenr) tuple,
-        where filename is a string and linenr an int."""
-        return (self.filename, self.linenr)
+        val = 0 if self.is_optional else 1
 
-    def get_visibility(self):
-        """Returns the visibility of the comment. See also
-        Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
+        if self.user_value is not None:
+            val = max(val, self.user_value)
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        val = min(val, self.visibility)
+
+        # Promote m to y for boolean choices
+        return 2 if val == 1 and self.type is BOOL else val
+
+    @property
+    def assignable(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_assignable is None:
+            self._cached_assignable = self._assignable()
+        return self._cached_assignable
+
+    @property
+    def visibility(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_vis is None:
+            self._cached_vis = _visibility(self)
+        return self._cached_vis
+
+    @property
+    def selection(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_selection is _NO_CACHED_SELECTION:
+            self._cached_selection = self._selection()
+        return self._cached_selection
+
+    def set_value(self, value):
+        """
+        Sets the user value (mode) of the choice. Like for Symbol.set_value(),
+        the visibility might truncate the value. Choices without the 'optional'
+        attribute (is_optional) can never be in n mode, but 0/"n" is still
+        accepted since it's not a malformed value (though it will have no
+        effect).
+
+        Returns True if the value is valid for the type of the choice, and
+        False otherwise. This only looks at the form of the value. Check the
+        Choice.assignable attribute to see what values are currently in range
+        and would actually be reflected in the mode of the choice.
+        """
+        if value in STR_TO_TRI:
+            value = STR_TO_TRI[value]
+
+        if value == self.user_value:
+            # We know the value must be valid if it was successfully set
+            # previously
+            self._was_set = True
+            return True
+
+        if not (self.orig_type is BOOL     and value in (2, 0) or
+                self.orig_type is TRISTATE and value in TRI_TO_STR):
+
+            # Display tristate values as n, m, y in the warning
+            self.kconfig._warn(
+                "the value {} is invalid for {}, which has type {} -- "
+                "assignment ignored"
+                .format(TRI_TO_STR[value] if value in TRI_TO_STR else
+                            "'{}'".format(value),
+                        _name_and_loc(self), TYPE_TO_STR[self.orig_type]))
+
+            return False
+
+        self.user_value = value
+        self._was_set = True
+        self._rec_invalidate()
+
+        return True
+
+    def unset_value(self):
+        """
+        Resets the user value (mode) and user selection of the Choice, as if
+        the user had never touched the mode or any of the choice symbols.
+        """
+        if self.user_value is not None or self.user_selection:
+            self.user_value = self.user_selection = None
+            self._rec_invalidate()
+
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        return {item for node in self.nodes for item in node.referenced}
+
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [d for node in self.nodes for d in node.orig_defaults]
+
+    def __repr__(self):
+        """
+        Returns a string with information about the choice when it is evaluated
+        on e.g. the interactive Python prompt.
+        """
+        fields = ["choice " + self.name if self.name else "choice",
+                  TYPE_TO_STR[self.type]]
+        add = fields.append
+
+        for node in self.nodes:
+            if node.prompt:
+                add('"{}"'.format(node.prompt[0]))
+
+        add("mode " + self.str_value)
+
+        if self.user_value is not None:
+            add('user mode {}'.format(TRI_TO_STR[self.user_value]))
+
+        if self.selection:
+            add("{} selected".format(self.selection.name))
+
+        if self.user_selection:
+            user_sel_str = "{} selected by user" \
+                           .format(self.user_selection.name)
+
+            if self.selection is not self.user_selection:
+                user_sel_str += " (overridden)"
+
+            add(user_sel_str)
+
+        add("visibility " + TRI_TO_STR[self.visibility])
+
+        if self.is_optional:
+            add("optional")
+
+        for node in self.nodes:
+            add("{}:{}".format(node.filename, node.linenr))
+
+        return "<{}>".format(", ".join(fields))
 
     def __str__(self):
-        """Returns a string containing various information about the
-        comment."""
-        dep_str = self.config._expr_val_str(self.orig_deps,
-                                            "(no dependencies)")
+        """
+        Returns a string representation of the choice when it is printed.
+        Matches the Kconfig format (though without the contained choice
+        symbols), with any parent dependencies propagated to the 'depends on'
+        condition.
 
-        additional_deps_str = " " + \
-          self.config._expr_val_str(self.deps_from_containing,
-                                    "(no additional dependencies)")
+        The returned string does not end in a newline.
 
-        return _lines("Comment",
-                      "Text: "         + str(self.text),
-                      "Dependencies: " + dep_str,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Location: {0}:{1}".format(self.filename, self.linenr))
+        See Symbol.__str__() as well.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like Choice.__str__(), but allows a custom format to be used for
+        all symbol/choice references. See expr_str().
+        """
+        return "\n\n".join(node.custom_str(sc_expr_str_fn)
+                           for node in self.nodes)
 
     #
     # Private methods
     #
 
     def __init__(self):
-        """Comment constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+        """
+        Choice constructor -- not intended to be called directly by Kconfiglib
+        clients.
+        """
+        # These attributes are always set on the instance from outside and
+        # don't need defaults:
+        #   direct_dep
+        #   kconfig
 
-        self.text = None
-        self.dep_expr = None
-        self.config = None
-        self.parent = None
+        # - UNKNOWN == 0
+        # - _visited is used during dep. loop detection
+        self.orig_type = self._visited = 0
 
-        # Dependency expression without dependencies from enclosing menus and
-        # ifs propagated
-        self.orig_deps = None
+        self.nodes = []
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this comment (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = None
+        self.syms = []
+        self.defaults = []
 
-        self.filename = None
-        self.linenr = None
+        self.name = \
+        self.user_value = self.user_selection = \
+        self._cached_vis = self._cached_assignable = None
 
-    def _make_conf(self, append_fn):
-        if self.config._eval_expr(self.dep_expr) != "n":
-            append_fn("\n#\n# {0}\n#".format(self.text))
+        self._cached_selection = _NO_CACHED_SELECTION
 
-class Kconfig_Syntax_Error(Exception):
-    """Exception raised for syntax errors."""
-    pass
+        # is_constant is checked by _make_depend_on(). Just set it to avoid
+        # having to special-case choices.
+        self.is_constant = self.is_optional = False
+
+        # See Kconfig._build_dep()
+        self._dependents = set()
+
+    def _assignable(self):
+        # Worker function for the 'assignable' attribute
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+
+        if not vis:
+            return ()
+
+        if vis == 2:
+            if not self.is_optional:
+                return (2,) if self.type is BOOL else (1, 2)
+            return (0, 2) if self.type is BOOL else (0, 1, 2)
+
+        # vis == 1
+
+        return (0, 1) if self.is_optional else (1,)
+
+    def _selection(self):
+        # Worker function for the 'selection' attribute
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        if self.tri_value != 2:
+            # Not in y mode, so no selection
+            return None
+
+        # Use the user selection if it's visible
+        if self.user_selection and self.user_selection.visibility:
+            return self.user_selection
+
+        # Otherwise, check if we have a default
+        return self._selection_from_defaults()
+
+    def _selection_from_defaults(self):
+        # Check if we have a default
+        for sym, cond in self.defaults:
+            # The default symbol must be visible too
+            if expr_value(cond) and sym.visibility:
+                return sym
+
+        # Otherwise, pick the first visible symbol, if any
+        for sym in self.syms:
+            if sym.visibility:
+                return sym
+
+        # Couldn't find a selection
+        return None
+
+    def _invalidate(self):
+        self._cached_vis = self._cached_assignable = None
+        self._cached_selection = _NO_CACHED_SELECTION
+
+    def _rec_invalidate(self):
+        # See Symbol._rec_invalidate()
+
+        self._invalidate()
+
+        for item in self._dependents:
+            if item._cached_vis is not None:
+                item._rec_invalidate()
+
+
+class MenuNode(object):
+    """
+    Represents a menu node in the configuration. This corresponds to an entry
+    in e.g. the 'make menuconfig' interface, though non-visible choices, menus,
+    and comments also get menu nodes. If a symbol or choice is defined in
+    multiple locations, it gets one menu node for each location.
+
+    The top-level menu node, corresponding to the implicit top-level menu, is
+    available in Kconfig.top_node.
+
+    The menu nodes for a Symbol or Choice can be found in the
+    Symbol/Choice.nodes attribute. Menus and comments are represented as plain
+    menu nodes, with their text stored in the prompt attribute (prompt[0]).
+    This mirrors the C implementation.
+
+    The following attributes are available on MenuNode instances. They should
+    be viewed as read-only.
+
+    item:
+      Either a Symbol, a Choice, or one of the constants MENU and COMMENT.
+      Menus and comments are represented as plain menu nodes. Ifs are collapsed
+      (matching the C implementation) and do not appear in the final menu tree.
+
+    next:
+      The following menu node. None if there is no following node.
+
+    list:
+      The first child menu node. None if there are no children.
+
+      Choices and menus naturally have children, but Symbols can also have
+      children because of menus created automatically from dependencies (see
+      kconfig-language.txt).
+
+    parent:
+      The parent menu node. None if there is no parent.
+
+    prompt:
+      A (string, cond) tuple with the prompt for the menu node and its
+      conditional expression (which is self.kconfig.y if there is no
+      condition). None if there is no prompt.
+
+      For symbols and choices, the prompt is stored in the MenuNode rather than
+      the Symbol or Choice instance. For menus and comments, the prompt holds
+      the text.
+
+    defaults:
+      The 'default' properties for this particular menu node. See
+      symbol.defaults.
+
+      When evaluating defaults, you should use Symbol/Choice.defaults instead,
+      as it include properties from all menu nodes (a symbol/choice can have
+      multiple definition locations/menu nodes). MenuNode.defaults is meant for
+      documentation generation.
+
+    selects:
+      Like MenuNode.defaults, for selects.
+
+    implies:
+      Like MenuNode.defaults, for implies.
+
+    ranges:
+      Like MenuNode.defaults, for ranges.
+
+    orig_prompt:
+    orig_defaults:
+    orig_selects:
+    orig_implies:
+    orig_ranges:
+      These work the like the corresponding attributes without orig_*, but omit
+      any dependencies propagated from 'depends on' and surrounding 'if's (the
+      direct dependencies, stored in MenuNode.dep).
+
+      One use for this is generating less cluttered documentation, by only
+      showing the direct dependencies in one place.
+
+    help:
+      The help text for the menu node for Symbols and Choices. None if there is
+      no help text. Always stored in the node rather than the Symbol or Choice.
+      It is possible to have a separate help text at each location if a symbol
+      is defined in multiple locations.
+
+      Trailing whitespace (including a final newline) is stripped from the help
+      text. This was not the case before Kconfiglib 10.21.0, where the format
+      was undocumented.
+
+    dep:
+      The direct ('depends on') dependencies for the menu node, or
+      self.kconfig.y if there are no direct dependencies.
+
+      This attribute includes any dependencies from surrounding menus and ifs.
+      Those get propagated to the direct dependencies, and the resulting direct
+      dependencies in turn get propagated to the conditions of all properties.
+
+      If a symbol or choice is defined in multiple locations, only the
+      properties defined at a particular location get the corresponding
+      MenuNode.dep dependencies propagated to them.
+
+    visibility:
+      The 'visible if' dependencies for the menu node (which must represent a
+      menu), or self.kconfig.y if there are no 'visible if' dependencies.
+      'visible if' dependencies are recursively propagated to the prompts of
+      symbols and choices within the menu.
+
+    referenced:
+      A set() with all symbols and choices referenced in the properties and
+      property conditions of the menu node.
+
+      Also includes dependencies inherited from surrounding menus and ifs.
+      Choices appear in the dependencies of choice symbols.
+
+    is_menuconfig:
+      Set to True if the children of the menu node should be displayed in a
+      separate menu. This is the case for the following items:
+
+        - Menus (node.item == MENU)
+
+        - Choices
+
+        - Symbols defined with the 'menuconfig' keyword. The children come from
+          implicitly created submenus, and should be displayed in a separate
+          menu rather than being indented.
+
+      'is_menuconfig' is just a hint on how to display the menu node. It's
+      ignored internally by Kconfiglib, except when printing symbols.
+
+    filename/linenr:
+      The location where the menu node appears. The filename is relative to
+      $srctree (or to the current directory if $srctree isn't set), except
+      absolute paths are used for paths outside $srctree.
+
+    include_path:
+      A tuple of (filename, linenr) tuples, giving the locations of the
+      'source' statements via which the Kconfig file containing this menu node
+      was included. The first element is the location of the 'source' statement
+      in the top-level Kconfig file passed to Kconfig.__init__(), etc.
+
+      Note that the Kconfig file of the menu node itself isn't included. Check
+      'filename' and 'linenr' for that.
+
+    kconfig:
+      The Kconfig instance the menu node is from.
+    """
+    __slots__ = (
+        "dep",
+        "filename",
+        "help",
+        "include_path",
+        "is_menuconfig",
+        "item",
+        "kconfig",
+        "linenr",
+        "list",
+        "next",
+        "parent",
+        "prompt",
+        "visibility",
+
+        # Properties
+        "defaults",
+        "selects",
+        "implies",
+        "ranges",
+    )
+
+    def __init__(self):
+        # Properties defined on this particular menu node. A local 'depends on'
+        # only applies to these, in case a symbol is defined in multiple
+        # locations.
+        self.defaults = []
+        self.selects = []
+        self.implies = []
+        self.ranges = []
+
+    @property
+    def orig_prompt(self):
+        """
+        See the class documentation.
+        """
+        if not self.prompt:
+            return None
+        return (self.prompt[0], self._strip_dep(self.prompt[1]))
+
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [(default, self._strip_dep(cond))
+                for default, cond in self.defaults]
+
+    @property
+    def orig_selects(self):
+        """
+        See the class documentation.
+        """
+        return [(select, self._strip_dep(cond))
+                for select, cond in self.selects]
+
+    @property
+    def orig_implies(self):
+        """
+        See the class documentation.
+        """
+        return [(imply, self._strip_dep(cond))
+                for imply, cond in self.implies]
+
+    @property
+    def orig_ranges(self):
+        """
+        See the class documentation.
+        """
+        return [(low, high, self._strip_dep(cond))
+                for low, high, cond in self.ranges]
+
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        # self.dep is included to catch dependencies from a lone 'depends on'
+        # when there are no properties to propagate it to
+        res = expr_items(self.dep)
+
+        if self.prompt:
+            res |= expr_items(self.prompt[1])
+
+        if self.item is MENU:
+            res |= expr_items(self.visibility)
+
+        for value, cond in self.defaults:
+            res |= expr_items(value)
+            res |= expr_items(cond)
+
+        for value, cond in self.selects:
+            res.add(value)
+            res |= expr_items(cond)
+
+        for value, cond in self.implies:
+            res.add(value)
+            res |= expr_items(cond)
+
+        for low, high, cond in self.ranges:
+            res.add(low)
+            res.add(high)
+            res |= expr_items(cond)
+
+        return res
+
+    def __repr__(self):
+        """
+        Returns a string with information about the menu node when it is
+        evaluated on e.g. the interactive Python prompt.
+        """
+        fields = []
+        add = fields.append
+
+        if self.item.__class__ is Symbol:
+            add("menu node for symbol " + self.item.name)
+
+        elif self.item.__class__ is Choice:
+            s = "menu node for choice"
+            if self.item.name is not None:
+                s += " " + self.item.name
+            add(s)
+
+        elif self.item is MENU:
+            add("menu node for menu")
+
+        else:  # self.item is COMMENT
+            add("menu node for comment")
+
+        if self.prompt:
+            add('prompt "{}" (visibility {})'.format(
+                self.prompt[0], TRI_TO_STR[expr_value(self.prompt[1])]))
+
+        if self.item.__class__ is Symbol and self.is_menuconfig:
+            add("is menuconfig")
+
+        add("deps " + TRI_TO_STR[expr_value(self.dep)])
+
+        if self.item is MENU:
+            add("'visible if' deps " + TRI_TO_STR[expr_value(self.visibility)])
+
+        if self.item.__class__ in _SYMBOL_CHOICE and self.help is not None:
+            add("has help")
+
+        if self.list:
+            add("has child")
+
+        if self.next:
+            add("has next")
+
+        add("{}:{}".format(self.filename, self.linenr))
+
+        return "<{}>".format(", ".join(fields))
+
+    def __str__(self):
+        """
+        Returns a string representation of the menu node. Matches the Kconfig
+        format, with any parent dependencies propagated to the 'depends on'
+        condition.
+
+        The output could (almost) be fed back into a Kconfig parser to redefine
+        the object associated with the menu node. See the module documentation
+        for a gotcha related to choice symbols.
+
+        For symbols and choices with multiple menu nodes (multiple definition
+        locations), properties that aren't associated with a particular menu
+        node are shown on all menu nodes ('option env=...', 'optional' for
+        choices, etc.).
+
+        The returned string does not end in a newline.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like MenuNode.__str__(), but allows a custom format to be used
+        for all symbol/choice references. See expr_str().
+        """
+        return self._menu_comment_node_str(sc_expr_str_fn) \
+               if self.item in _MENU_COMMENT else \
+               self._sym_choice_node_str(sc_expr_str_fn)
+
+    def _menu_comment_node_str(self, sc_expr_str_fn):
+        s = '{} "{}"'.format("menu" if self.item is MENU else "comment",
+                             self.prompt[0])
+
+        if self.dep is not self.kconfig.y:
+            s += "\n\tdepends on {}".format(expr_str(self.dep, sc_expr_str_fn))
+
+        if self.item is MENU and self.visibility is not self.kconfig.y:
+            s += "\n\tvisible if {}".format(expr_str(self.visibility,
+                                                     sc_expr_str_fn))
+
+        return s
+
+    def _sym_choice_node_str(self, sc_expr_str_fn):
+        def indent_add(s):
+            lines.append("\t" + s)
+
+        def indent_add_cond(s, cond):
+            if cond is not self.kconfig.y:
+                s += " if " + expr_str(cond, sc_expr_str_fn)
+            indent_add(s)
+
+        sc = self.item
+
+        if sc.__class__ is Symbol:
+            lines = [("menuconfig " if self.is_menuconfig else "config ")
+                     + sc.name]
+        else:
+            lines = ["choice " + sc.name if sc.name else "choice"]
+
+        if sc.orig_type and not self.prompt:  # sc.orig_type != UNKNOWN
+            # If there's a prompt, we'll use the '<type> "prompt"' shorthand
+            # instead
+            indent_add(TYPE_TO_STR[sc.orig_type])
+
+        if self.prompt:
+            if sc.orig_type:
+                prefix = TYPE_TO_STR[sc.orig_type]
+            else:
+                # Symbol defined without a type (which generates a warning)
+                prefix = "prompt"
+
+            indent_add_cond(prefix + ' "{}"'.format(escape(self.prompt[0])),
+                            self.orig_prompt[1])
+
+        if sc.__class__ is Symbol:
+            if sc.is_allnoconfig_y:
+                indent_add("option allnoconfig_y")
+
+            if sc is sc.kconfig.defconfig_list:
+                indent_add("option defconfig_list")
+
+            if sc.env_var is not None:
+                indent_add('option env="{}"'.format(sc.env_var))
+
+            if sc is sc.kconfig.modules:
+                indent_add("option modules")
+
+            for low, high, cond in self.orig_ranges:
+                indent_add_cond(
+                    "range {} {}".format(sc_expr_str_fn(low),
+                                         sc_expr_str_fn(high)),
+                    cond)
+
+        for default, cond in self.orig_defaults:
+            indent_add_cond("default " + expr_str(default, sc_expr_str_fn),
+                            cond)
+
+        if sc.__class__ is Choice and sc.is_optional:
+            indent_add("optional")
+
+        if sc.__class__ is Symbol:
+            for select, cond in self.orig_selects:
+                indent_add_cond("select " + sc_expr_str_fn(select), cond)
+
+            for imply, cond in self.orig_implies:
+                indent_add_cond("imply " + sc_expr_str_fn(imply), cond)
+
+        if self.dep is not sc.kconfig.y:
+            indent_add("depends on " + expr_str(self.dep, sc_expr_str_fn))
+
+        if self.help is not None:
+            indent_add("help")
+            for line in self.help.splitlines():
+                indent_add("  " + line)
+
+        return "\n".join(lines)
+
+    def _strip_dep(self, expr):
+        # Helper function for removing MenuNode.dep from 'expr'. Uses two
+        # pieces of internal knowledge: (1) Expressions are reused rather than
+        # copied, and (2) the direct dependencies always appear at the end.
+
+        # ... if dep -> ... if y
+        if self.dep is expr:
+            return self.kconfig.y
+
+        # (AND, X, dep) -> X
+        if expr.__class__ is tuple and expr[0] is AND and expr[2] is self.dep:
+            return expr[1]
+
+        return expr
+
+
+class Variable(object):
+    """
+    Represents a preprocessor variable/function.
+
+    The following attributes are available:
+
+    name:
+      The name of the variable.
+
+    value:
+      The unexpanded value of the variable.
+
+    expanded_value:
+      The expanded value of the variable. For simple variables (those defined
+      with :=), this will equal 'value'. Accessing this property will raise a
+      KconfigError if the expansion seems to be stuck in a loop.
+
+      Accessing this field is the same as calling expanded_value_w_args() with
+      no arguments. I hadn't considered function arguments when adding it. It
+      is retained for backwards compatibility though.
+
+    is_recursive:
+      True if the variable is recursive (defined with =).
+    """
+    __slots__ = (
+        "_n_expansions",
+        "is_recursive",
+        "kconfig",
+        "name",
+        "value",
+    )
+
+    @property
+    def expanded_value(self):
+        """
+        See the class documentation.
+        """
+        return self.expanded_value_w_args()
+
+    def expanded_value_w_args(self, *args):
+        """
+        Returns the expanded value of the variable/function. Any arguments
+        passed will be substituted for $(1), $(2), etc.
+
+        Raises a KconfigError if the expansion seems to be stuck in a loop.
+        """
+        return self.kconfig._fn_val((self.name,) + args)
+
+    def __repr__(self):
+        return "<variable {}, {}, value '{}'>" \
+               .format(self.name,
+                       "recursive" if self.is_recursive else "immediate",
+                       self.value)
+
+
+class KconfigError(Exception):
+    """
+    Exception raised for Kconfig-related errors.
+
+    KconfigError and KconfigSyntaxError are the same class. The
+    KconfigSyntaxError alias is only maintained for backwards compatibility.
+    """
+
+KconfigSyntaxError = KconfigError  # Backwards compatibility
+
+
+class InternalError(Exception):
+    "Never raised. Kept around for backwards compatibility."
+
+
+# Workaround:
+#
+# If 'errno' and 'strerror' are set on IOError, then __str__() always returns
+# "[Errno <errno>] <strerror>", ignoring any custom message passed to the
+# constructor. By defining our own subclass, we can use a custom message while
+# also providing 'errno', 'strerror', and 'filename' to scripts.
+class _KconfigIOError(IOError):
+    def __init__(self, ioerror, msg):
+        self.msg = msg
+        super(_KconfigIOError, self).__init__(
+            ioerror.errno, ioerror.strerror, ioerror.filename)
+
+    def __str__(self):
+        return self.msg
 
-class Internal_Error(Exception):
-    """Exception raised for internal errors."""
-    pass
 
 #
 # Public functions
 #
 
-def tri_less(v1, v2):
-    """Returns True if the tristate v1 is less than the tristate v2, where "n",
-    "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] < TRI_TO_INT[v2]
 
-def tri_less_eq(v1, v2):
-    """Returns True if the tristate v1 is less than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] <= TRI_TO_INT[v2]
+def expr_value(expr):
+    """
+    Evaluates the expression 'expr' to a tristate value. Returns 0 (n), 1 (m),
+    or 2 (y).
 
-def tri_greater(v1, v2):
-    """Returns True if the tristate v1 is greater than the tristate v2, where
-    "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] > TRI_TO_INT[v2]
+    'expr' must be an already-parsed expression from a Symbol, Choice, or
+    MenuNode property. To evaluate an expression represented as a string, use
+    Kconfig.eval_string().
 
-def tri_greater_eq(v1, v2):
-    """Returns True if the tristate v1 is greater than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] >= TRI_TO_INT[v2]
+    Passing subexpressions of expressions to this function works as expected.
+    """
+    if expr.__class__ is not tuple:
+        return expr.tri_value
 
-#
-# Internal classes
-#
+    if expr[0] is AND:
+        v1 = expr_value(expr[1])
+        # Short-circuit the n case as an optimization (~5% faster
+        # allnoconfig.py and allyesconfig.py, as of writing)
+        return 0 if not v1 else min(v1, expr_value(expr[2]))
 
-class _Feed(object):
+    if expr[0] is OR:
+        v1 = expr_value(expr[1])
+        # Short-circuit the y case as an optimization
+        return 2 if v1 == 2 else max(v1, expr_value(expr[2]))
 
-    """Class for working with sequences in a stream-like fashion; handy for
-    tokens."""
+    if expr[0] is NOT:
+        return 2 - expr_value(expr[1])
 
-    # This would be more helpful on the item classes, but would remove some
-    # flexibility
-    __slots__ = ['items', 'length', 'i']
+    # Relation
+    #
+    # Implements <, <=, >, >= comparisons as well. These were added to
+    # kconfig in 31847b67 (kconfig: allow use of relations other than
+    # (in)equality).
 
-    def __init__(self, items):
-        self.items = items
-        self.length = len(self.items)
-        self.i = 0
+    rel, v1, v2 = expr
 
-    def get_next(self):
-        if self.i >= self.length:
-            return None
-        item = self.items[self.i]
-        self.i += 1
-        return item
+    # If both operands are strings...
+    if v1.orig_type is STRING and v2.orig_type is STRING:
+        # ...then compare them lexicographically
+        comp = _strcmp(v1.str_value, v2.str_value)
+    else:
+        # Otherwise, try to compare them as numbers
+        try:
+            comp = _sym_to_num(v1) - _sym_to_num(v2)
+        except ValueError:
+            # Fall back on a lexicographic comparison if the operands don't
+            # parse as numbers
+            comp = _strcmp(v1.str_value, v2.str_value)
 
-    def peek_next(self):
-        return None if self.i >= self.length else self.items[self.i]
+    return 2*(comp == 0 if rel is EQUAL else
+              comp != 0 if rel is UNEQUAL else
+              comp <  0 if rel is LESS else
+              comp <= 0 if rel is LESS_EQUAL else
+              comp >  0 if rel is GREATER else
+              comp >= 0)
 
-    def check(self, token):
-        """Check if the next token is 'token'. If so, remove it from the token
-        feed and return True. Otherwise, leave it in and return False."""
-        if self.i < self.length and self.items[self.i] == token:
-            self.i += 1
-            return True
-        return False
 
-    def unget_all(self):
-        self.i = 0
+def standard_sc_expr_str(sc):
+    """
+    Standard symbol/choice printing function. Uses plain Kconfig syntax, and
+    displays choices as <choice> (or <choice NAME>, for named choices).
 
-class _FileFeed(object):
+    See expr_str().
+    """
+    if sc.__class__ is Symbol:
+        if sc.is_constant and sc.name not in STR_TO_TRI:
+            return '"{}"'.format(escape(sc.name))
+        return sc.name
 
-    """Feeds lines from a file. Keeps track of the filename and current line
-    number. Joins any line ending in \\ with the following line. We need to be
-    careful to get the line number right in the presence of continuation
-    lines."""
+    return "<choice {}>".format(sc.name) if sc.name else "<choice>"
 
-    __slots__ = ['filename', 'lines', 'length', 'linenr']
 
-    def __init__(self, filename):
-        self.filename = _clean_up_path(filename)
-        with open(filename, "r") as f:
-            # No interleaving of I/O and processing yet. Don't know if it would
-            # help.
-            self.lines = f.readlines()
-        self.length = len(self.lines)
-        self.linenr = 0
+def expr_str(expr, sc_expr_str_fn=standard_sc_expr_str):
+    """
+    Returns the string representation of the expression 'expr', as in a Kconfig
+    file.
 
-    def get_next(self):
-        if self.linenr >= self.length:
-            return None
-        line = self.lines[self.linenr]
-        self.linenr += 1
-        while line.endswith("\\\n"):
-            line = line[:-2] + self.lines[self.linenr]
-            self.linenr += 1
-        return line
+    Passing subexpressions of expressions to this function works as expected.
 
-    def peek_next(self):
-        linenr = self.linenr
-        if linenr >= self.length:
-            return None
-        line = self.lines[linenr]
-        while line.endswith("\\\n"):
-            linenr += 1
-            line = line[:-2] + self.lines[linenr]
-        return line
+    sc_expr_str_fn (default: standard_sc_expr_str):
+      This function is called for every symbol/choice (hence "sc") appearing in
+      the expression, with the symbol/choice as the argument. It is expected to
+      return a string to be used for the symbol/choice.
 
-    def unget(self):
-        self.linenr -= 1
-        while self.lines[self.linenr].endswith("\\\n"):
-            self.linenr -= 1
+      This can be used e.g. to turn symbols/choices into links when generating
+      documentation, or for printing the value of each symbol/choice after it.
+
+      Note that quoted values are represented as constants symbols
+      (Symbol.is_constant == True).
+    """
+    if expr.__class__ is not tuple:
+        return sc_expr_str_fn(expr)
+
+    if expr[0] is AND:
+        return "{} && {}".format(_parenthesize(expr[1], OR, sc_expr_str_fn),
+                                 _parenthesize(expr[2], OR, sc_expr_str_fn))
+
+    if expr[0] is OR:
+        # This turns A && B || C && D into "(A && B) || (C && D)", which is
+        # redundant, but more readable
+        return "{} || {}".format(_parenthesize(expr[1], AND, sc_expr_str_fn),
+                                 _parenthesize(expr[2], AND, sc_expr_str_fn))
+
+    if expr[0] is NOT:
+        if expr[1].__class__ is tuple:
+            return "!({})".format(expr_str(expr[1], sc_expr_str_fn))
+        return "!" + sc_expr_str_fn(expr[1])  # Symbol
+
+    # Relation
+    #
+    # Relation operands are always symbols (quoted strings are constant
+    # symbols)
+    return "{} {} {}".format(sc_expr_str_fn(expr[1]), REL_TO_STR[expr[0]],
+                             sc_expr_str_fn(expr[2]))
+
+
+def expr_items(expr):
+    """
+    Returns a set() of all items (symbols and choices) that appear in the
+    expression 'expr'.
+
+    Passing subexpressions of expressions to this function works as expected.
+    """
+    res = set()
+
+    def rec(subexpr):
+        if subexpr.__class__ is tuple:
+            # AND, OR, NOT, or relation
+
+            rec(subexpr[1])
+
+            # NOTs only have a single operand
+            if subexpr[0] is not NOT:
+                rec(subexpr[2])
+
+        else:
+            # Symbol or choice
+            res.add(subexpr)
+
+    rec(expr)
+    return res
+
+
+def split_expr(expr, op):
+    """
+    Returns a list containing the top-level AND or OR operands in the
+    expression 'expr', in the same (left-to-right) order as they appear in
+    the expression.
+
+    This can be handy e.g. for splitting (weak) reverse dependencies
+    from 'select' and 'imply' into individual selects/implies.
+
+    op:
+      Either AND to get AND operands, or OR to get OR operands.
+
+      (Having this as an operand might be more future-safe than having two
+      hardcoded functions.)
+
+
+    Pseudo-code examples:
+
+      split_expr( A                    , OR  )  ->  [A]
+      split_expr( A && B               , OR  )  ->  [A && B]
+      split_expr( A || B               , OR  )  ->  [A, B]
+      split_expr( A || B               , AND )  ->  [A || B]
+      split_expr( A || B || (C && D)   , OR  )  ->  [A, B, C && D]
+
+      # Second || is not at the top level
+      split_expr( A || (B && (C || D)) , OR )  ->  [A, B && (C || D)]
+
+      # Parentheses don't matter as long as we stay at the top level (don't
+      # encounter any non-'op' nodes)
+      split_expr( (A || B) || C        , OR )  ->  [A, B, C]
+      split_expr( A || (B || C)        , OR )  ->  [A, B, C]
+    """
+    res = []
+
+    def rec(subexpr):
+        if subexpr.__class__ is tuple and subexpr[0] is op:
+            rec(subexpr[1])
+            rec(subexpr[2])
+        else:
+            res.append(subexpr)
+
+    rec(expr)
+    return res
+
+
+def escape(s):
+    r"""
+    Escapes the string 's' in the same fashion as is done for display in
+    Kconfig format and when writing strings to a .config file. " and \ are
+    replaced by \" and \\, respectively.
+    """
+    # \ must be escaped before " to avoid double escaping
+    return s.replace("\\", r"\\").replace('"', r'\"')
+
+
+def unescape(s):
+    r"""
+    Unescapes the string 's'. \ followed by any character is replaced with just
+    that character. Used internally when reading .config files.
+    """
+    return _unescape_sub(r"\1", s)
+
+# unescape() helper
+_unescape_sub = re.compile(r"\\(.)").sub
+
+
+def standard_kconfig():
+    """
+    Helper for tools. Loads the top-level Kconfig specified as the first
+    command-line argument, or "Kconfig" if there are no command-line arguments.
+    Returns the Kconfig instance.
+
+    Exits with sys.exit() (which raises a SystemExit exception) and prints a
+    usage note to stderr if more than one command-line argument is passed.
+    """
+    if len(sys.argv) > 2:
+        sys.exit("usage: {} [Kconfig]".format(sys.argv[0]))
+
+    # Only show backtraces for unexpected exceptions
+    try:
+        return Kconfig("Kconfig" if len(sys.argv) < 2 else sys.argv[1])
+    except (EnvironmentError, KconfigError) as e:
+        # Some long exception messages have extra newlines for better
+        # formatting when reported as an unhandled exception. Strip them here.
+        sys.exit(str(e).strip())
+
+
+def standard_config_filename():
+    """
+    Helper for tools. Returns the value of KCONFIG_CONFIG (which specifies the
+    .config file to load/save) if it is set, and ".config" otherwise.
+
+    Calling load_config() with filename=None might give the behavior you want,
+    without having to use this function.
+    """
+    return os.getenv("KCONFIG_CONFIG", ".config")
+
+
+def load_allconfig(kconf, filename):
+    """
+    Helper for all*config. Loads (merges) the configuration file specified by
+    KCONFIG_ALLCONFIG, if any. See Documentation/kbuild/kconfig.txt in the
+    Linux kernel.
+
+    Disables warnings for duplicated assignments within configuration files for
+    the duration of the call (kconf.warn_assign_override/warn_assign_redun = False),
+    and restores the previous warning settings at the end. The
+    KCONFIG_ALLCONFIG configuration file is expected to override symbols.
+
+    Exits with sys.exit() (which raises a SystemExit exception) and prints an
+    error to stderr if KCONFIG_ALLCONFIG is set but the configuration file
+    can't be opened.
+
+    kconf:
+      Kconfig instance to load the configuration in.
+
+    filename:
+      Command-specific configuration filename - "allyes.config",
+      "allno.config", etc.
+    """
+    allconfig = os.getenv("KCONFIG_ALLCONFIG")
+    if allconfig is None:
+        return
+
+    def std_msg(e):
+        # "Upcasts" a _KconfigIOError to an IOError, removing the custom
+        # __str__() message. The standard message is better here.
+        #
+        # This might also convert an OSError to an IOError in obscure cases,
+        # but it's probably not a big deal. The distinction is shaky (see
+        # PEP-3151).
+        return IOError(e.errno, e.strerror, e.filename)
+
+    old_warn_assign_override = kconf.warn_assign_override
+    old_warn_assign_redun = kconf.warn_assign_redun
+    kconf.warn_assign_override = kconf.warn_assign_redun = False
+
+    if allconfig in ("", "1"):
+        try:
+            print(kconf.load_config(filename, False))
+        except EnvironmentError as e1:
+            try:
+                print(kconf.load_config("all.config", False))
+            except EnvironmentError as e2:
+                sys.exit("error: KCONFIG_ALLCONFIG is set, but neither {} "
+                         "nor all.config could be opened: {}, {}"
+                         .format(filename, std_msg(e1), std_msg(e2)))
+    else:
+        try:
+            print(kconf.load_config(allconfig, False))
+        except EnvironmentError as e:
+            sys.exit("error: KCONFIG_ALLCONFIG is set to '{}', which "
+                     "could not be opened: {}"
+                     .format(allconfig, std_msg(e)))
+
+    kconf.warn_assign_override = old_warn_assign_override
+    kconf.warn_assign_redun = old_warn_assign_redun
 
-    def next_nonblank(self):
-        """Removes lines up to and including the next non-blank (not all-space)
-        line and returns it. Returns None if there are no more non-blank
-        lines."""
-        while 1:
-            line = self.get_next()
-            if line is None or not line.isspace():
-                return line
 
 #
 # Internal functions
 #
 
-def _get_visibility(sc):
-    """Symbols and Choices have a "visibility" that acts as an upper bound on
-    the values a user can set for them, corresponding to the visibility in e.g.
-    'make menuconfig'. This function calculates the visibility for the Symbol
-    or Choice 'sc' -- the logic is nearly identical."""
-    if sc.cached_visibility is None:
-        vis = "n"
-        for _, cond_expr in sc.prompts:
-            vis = sc.config._eval_max(vis, cond_expr)
 
-        if isinstance(sc, Symbol) and sc.is_choice_sym:
-            if sc.type == TRISTATE and vis == "m" and \
-               sc.parent.get_mode() == "y":
-                # Choice symbols with visibility "m" are not visible if the
-                # choice has mode "y"
-                vis = "n"
-            else:
-                vis = sc.config._eval_min(vis, _get_visibility(sc.parent))
+def _visibility(sc):
+    # Symbols and Choices have a "visibility" that acts as an upper bound on
+    # the values a user can set for them, corresponding to the visibility in
+    # e.g. 'make menuconfig'. This function calculates the visibility for the
+    # Symbol or Choice 'sc' -- the logic is nearly identical.
 
-        # Promote "m" to "y" if we're dealing with a non-tristate
-        if vis == "m" and sc.type != TRISTATE:
-            vis = "y"
+    vis = 0
 
-        sc.cached_visibility = vis
+    for node in sc.nodes:
+        if node.prompt:
+            vis = max(vis, expr_value(node.prompt[1]))
 
-    return sc.cached_visibility
+    if sc.__class__ is Symbol and sc.choice:
+        if sc.choice.orig_type is TRISTATE and \
+           sc.orig_type is not TRISTATE and sc.choice.tri_value != 2:
+            # Non-tristate choice symbols are only visible in y mode
+            return 0
 
-def _make_and(e1, e2):
-    """Constructs an AND (&&) expression. Performs trivial simplification.
-    Nones equate to 'y'.
+        if sc.orig_type is TRISTATE and vis == 1 and sc.choice.tri_value == 2:
+            # Choice symbols with m visibility are not visible in y mode
+            return 0
 
-    Note: returns None if e1 == e2 == None."""
-    if e1 is None or e1 == "y":
-        return e2
-    if e2 is None or e2 == "y":
-        return e1
+    # Promote m to y if we're dealing with a non-tristate (possibly due to
+    # modules being disabled)
+    if vis == 1 and sc.type is not TRISTATE:
+        return 2
 
-    # Prefer to merge argument lists if possible to reduce the number of nodes
+    return vis
 
-    if isinstance(e1, tuple) and e1[0] == AND:
-        if isinstance(e2, tuple) and e2[0] == AND:
-            return (AND, e1[1] + e2[1])
-        return (AND, e1[1] + [e2])
 
-    if isinstance(e2, tuple) and e2[0] == AND:
-        return (AND, e2[1] + [e1])
+def _make_depend_on(sc, expr):
+    # Adds 'sc' (symbol or choice) as a "dependee" to all symbols in 'expr'.
+    # Constant symbols in 'expr' are skipped as they can never change value
+    # anyway.
 
-    return (AND, [e1, e2])
+    if expr.__class__ is tuple:
+        # AND, OR, NOT, or relation
 
-def _make_or(e1, e2):
-    """Constructs an OR (||) expression. Performs trivial simplification and
-    avoids Nones. Nones equate to 'y', which is usually what we want, but needs
-    to be kept in mind."""
+        _make_depend_on(sc, expr[1])
 
-    # Perform trivial simplification and avoid None's (which
-    # correspond to y's)
-    if e1 is None or e2 is None or e1 == "y" or e2 == "y":
-        return "y"
-    if e1 == "n":
-        return e2
+        # NOTs only have a single operand
+        if expr[0] is not NOT:
+            _make_depend_on(sc, expr[2])
 
-    # Prefer to merge argument lists if possible to reduce the number of nodes
+    elif not expr.is_constant:
+        # Non-constant symbol, or choice
+        expr._dependents.add(sc)
 
-    if isinstance(e1, tuple) and e1[0] == OR:
-        if isinstance(e2, tuple) and e2[0] == OR:
-            return (OR, e1[1] + e2[1])
-        return (OR, e1[1] + [e2])
 
-    if isinstance(e2, tuple) and e2[0] == OR:
-        return (OR, e2[1] + [e1])
+def _parenthesize(expr, type_, sc_expr_str_fn):
+    # expr_str() helper. Adds parentheses around expressions of type 'type_'.
 
-    return (OR, [e1, e2])
+    if expr.__class__ is tuple and expr[0] is type_:
+        return "({})".format(expr_str(expr, sc_expr_str_fn))
+    return expr_str(expr, sc_expr_str_fn)
 
-def _get_expr_syms_rec(expr, res):
-    """_get_expr_syms() helper. Recurses through expressions."""
-    if isinstance(expr, Symbol):
-        res.add(expr)
-    elif isinstance(expr, str):
-        return
-    elif expr[0] == AND or expr[0] == OR:
-        for term in expr[1]:
-            _get_expr_syms_rec(term, res)
-    elif expr[0] == NOT:
-        _get_expr_syms_rec(expr[1], res)
-    elif expr[0] == EQUAL or expr[0] == UNEQUAL:
-        if isinstance(expr[1], Symbol):
-            res.add(expr[1])
-        if isinstance(expr[2], Symbol):
-            res.add(expr[2])
-    else:
-        _internal_error("Internal error while fetching symbols from an "
-                        "expression with token stream {0}.".format(expr))
 
-def _get_expr_syms(expr):
-    """Returns the set() of symbols appearing in expr."""
-    res = set()
-    if expr is not None:
-        _get_expr_syms_rec(expr, res)
-    return res
+def _ordered_unique(lst):
+    # Returns 'lst' with any duplicates removed, preserving order. This hacky
+    # version seems to be a common idiom. It relies on short-circuit evaluation
+    # and set.add() returning None, which is falsy.
 
-def _str_val(obj):
-    """Returns the value of obj as a string. If obj is not a string (constant
-    symbol), it must be a Symbol."""
-    return obj if isinstance(obj, str) else obj.get_value()
+    seen = set()
+    seen_add = seen.add
+    return [x for x in lst if x not in seen and not seen_add(x)]
 
-def _make_block_conf(block, append_fn):
-    """Returns a list of .config strings for a block (list) of items."""
-
-    # Collect the substrings in a list and later use join() instead of += to
-    # build the final .config contents. With older Python versions, this yields
-    # linear instead of quadratic complexity.
-    for item in block:
-        item._make_conf(append_fn)
-
-def _sym_str_string(sym_or_str):
-    if isinstance(sym_or_str, str):
-        return '"' + sym_or_str + '"'
-    return sym_or_str.name
-
-def _intersperse(lst, op):
-    """_expr_to_str() helper. Gets the string representation of each expression
-    in lst and produces a list where op has been inserted between the
-    elements."""
-    if not lst:
-        return ""
-
-    res = []
-
-    def handle_sub_expr(expr):
-        no_parens = isinstance(expr, (str, Symbol)) or \
-                    expr[0] in (EQUAL, UNEQUAL) or \
-                    PRECEDENCE[op] <= PRECEDENCE[expr[0]]
-        if not no_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr))
-        if not no_parens:
-            res.append(")")
-
-    op_str = OP_TO_STR[op]
-
-    handle_sub_expr(lst[0])
-    for expr in lst[1:]:
-        res.append(op_str)
-        handle_sub_expr(expr)
-
-    return res
-
-def _expr_to_str_rec(expr):
-    if expr is None:
-        return [""]
-
-    if isinstance(expr, (Symbol, str)):
-        return [_sym_str_string(expr)]
-
-    if expr[0] in (AND, OR):
-        return _intersperse(expr[1], expr[0])
-
-    if expr[0] == NOT:
-        need_parens = not isinstance(expr[1], (str, Symbol))
-
-        res = ["!"]
-        if need_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr[1]))
-        if need_parens:
-            res.append(")")
-        return res
-
-    if expr[0] in (EQUAL, UNEQUAL):
-        return [_sym_str_string(expr[1]),
-                OP_TO_STR[expr[0]],
-                _sym_str_string(expr[2])]
-
-def _expr_to_str(expr):
-    return "".join(_expr_to_str_rec(expr))
-
-def _indentation(line):
-    """Returns the length of the line's leading whitespace, treating tab stops
-    as being spaced 8 characters apart."""
-    line = line.expandtabs()
-    return len(line) - len(line.lstrip())
-
-def _deindent(line, indent):
-    """Deindent 'line' by 'indent' spaces."""
-    line = line.expandtabs()
-    if len(line) <= indent:
-        return line
-    return line[indent:]
 
 def _is_base_n(s, n):
     try:
@@ -3412,133 +6222,809 @@ def _is_base_n(s, n):
     except ValueError:
         return False
 
-def _lines(*args):
-    """Returns a string consisting of all arguments, with newlines inserted
-    between them."""
-    return "\n".join(args)
 
-def _comment(s):
-    """Returns a new string with "#" inserted before each line in 's'."""
-    if not s:
-        return "#"
-    res = "".join(["#" + line for line in s.splitlines(True)])
-    if s.endswith("\n"):
-        return res + "#"
-    return res
+def _strcmp(s1, s2):
+    # strcmp()-alike that returns -1, 0, or 1
 
-def _clean_up_path(path):
-    """Strips an initial "./" and any trailing slashes from 'path'."""
-    if path.startswith("./"):
-        path = path[2:]
-    return path.rstrip("/")
+    return (s1 > s2) - (s1 < s2)
 
-def _build_msg(msg, filename, linenr):
-    if filename is not None:
-        msg = "{0}:{1}: ".format(_clean_up_path(filename), linenr) + msg
-    return msg
 
-def _stderr_msg(msg, filename, linenr):
-    sys.stderr.write(_build_msg(msg, filename, linenr) + "\n")
+def _sym_to_num(sym):
+    # expr_value() helper for converting a symbol to a number. Raises
+    # ValueError for symbols that can't be converted.
 
-def _tokenization_error(s, filename, linenr):
-    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
-    raise Kconfig_Syntax_Error("{0}Couldn't tokenize '{1}'"
-                               .format(loc, s.strip()))
+    # For BOOL and TRISTATE, n/m/y count as 0/1/2. This mirrors 9059a3493ef
+    # ("kconfig: fix relational operators for bool and tristate symbols") in
+    # the C implementation.
+    return sym.tri_value if sym.orig_type in _BOOL_TRISTATE else \
+           int(sym.str_value, _TYPE_TO_BASE[sym.orig_type])
 
-def _parse_error(s, msg, filename, linenr):
-    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
-    raise Kconfig_Syntax_Error("{0}Couldn't parse '{1}'{2}"
-                               .format(loc, s.strip(),
-                                       "." if msg is None else ": " + msg))
 
-def _internal_error(msg):
-    raise Internal_Error(msg +
-      "\nSorry! You may want to send an email to ulfalizer a.t Google's "
-      "email service to tell me about this. Include the message above and the "
-      "stack trace and describe what you were doing.")
+def _touch_dep_file(path, sym_name):
+    # If sym_name is MY_SYM_NAME, touches my/sym/name.h. See the sync_deps()
+    # docstring.
+
+    sym_path = path + os.sep + sym_name.lower().replace("_", os.sep) + ".h"
+    sym_path_dir = dirname(sym_path)
+    if not exists(sym_path_dir):
+        os.makedirs(sym_path_dir, 0o755)
+
+    # A kind of truncating touch, mirroring the C tools
+    os.close(os.open(
+        sym_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o644))
+
+
+def _save_old(path):
+    # See write_config()
+
+    def copy(src, dst):
+        # Import as needed, to save some startup time
+        import shutil
+        shutil.copyfile(src, dst)
+
+    if islink(path):
+        # Preserve symlinks
+        copy_fn = copy
+    elif hasattr(os, "replace"):
+        # Python 3 (3.3+) only. Best choice when available, because it
+        # removes <filename>.old on both *nix and Windows.
+        copy_fn = os.replace
+    elif os.name == "posix":
+        # Removes <filename>.old on POSIX systems
+        copy_fn = os.rename
+    else:
+        # Fall back on copying
+        copy_fn = copy
+
+    try:
+        copy_fn(path, path + ".old")
+    except Exception:
+        # Ignore errors from 'path' missing as well as other errors.
+        # <filename>.old file is usually more of a nice-to-have, and not worth
+        # erroring out over e.g. if <filename>.old happens to be a directory or
+        # <filename> is something like /dev/null.
+        pass
+
+
+def _name_and_loc(sc):
+    # Helper for giving the symbol/choice name and location(s) in e.g. warnings
+
+    # Reuse the expression format. That way choices show up as
+    # '<choice (name, if any)>'
+    name = standard_sc_expr_str(sc)
+
+    if not sc.nodes:
+        return name + " (undefined)"
+
+    return "{} (defined at {})".format(
+        name,
+        ", ".join("{}:{}".format(node.filename, node.linenr)
+                  for node in sc.nodes))
+
+
+# Menu manipulation
+
+
+def _expr_depends_on(expr, sym):
+    # Reimplementation of expr_depends_symbol() from mconf.c. Used to determine
+    # if a submenu should be implicitly created. This also influences which
+    # items inside choice statements are considered choice items.
+
+    if expr.__class__ is not tuple:
+        return expr is sym
+
+    if expr[0] in _EQUAL_UNEQUAL:
+        # Check for one of the following:
+        # sym = m/y, m/y = sym, sym != n, n != sym
+
+        left, right = expr[1:]
+
+        if right is sym:
+            left, right = right, left
+        elif left is not sym:
+            return False
+
+        return (expr[0] is EQUAL and right is sym.kconfig.m or
+                                     right is sym.kconfig.y) or \
+               (expr[0] is UNEQUAL and right is sym.kconfig.n)
+
+    return expr[0] is AND and \
+           (_expr_depends_on(expr[1], sym) or
+            _expr_depends_on(expr[2], sym))
+
+
+def _auto_menu_dep(node1, node2):
+    # Returns True if node2 has an "automatic menu dependency" on node1. If
+    # node2 has a prompt, we check its condition. Otherwise, we look directly
+    # at node2.dep.
+
+    return _expr_depends_on(node2.prompt[1] if node2.prompt else node2.dep,
+                            node1.item)
+
+
+def _flatten(node):
+    # "Flattens" menu nodes without prompts (e.g. 'if' nodes and non-visible
+    # symbols with children from automatic menu creation) so that their
+    # children appear after them instead. This gives a clean menu structure
+    # with no unexpected "jumps" in the indentation.
+    #
+    # Do not flatten promptless choices (which can appear "legitimately" if a
+    # named choice is defined in multiple locations to add on symbols). It
+    # looks confusing, and the menuconfig already shows all choice symbols if
+    # you enter the choice at some location with a prompt.
+
+    while node:
+        if node.list and not node.prompt and \
+           node.item.__class__ is not Choice:
+
+            last_node = node.list
+            while 1:
+                last_node.parent = node.parent
+                if not last_node.next:
+                    break
+                last_node = last_node.next
+
+            last_node.next = node.next
+            node.next = node.list
+            node.list = None
+
+        node = node.next
+
+
+def _remove_ifs(node):
+    # Removes 'if' nodes (which can be recognized by MenuNode.item being None),
+    # which are assumed to already have been flattened. The C implementation
+    # doesn't bother to do this, but we expose the menu tree directly, and it
+    # makes it nicer to work with.
+
+    cur = node.list
+    while cur and not cur.item:
+        cur = cur.next
+
+    node.list = cur
+
+    while cur:
+        next = cur.next
+        while next and not next.item:
+            next = next.next
+
+        # Equivalent to
+        #
+        #   cur.next = next
+        #   cur = next
+        #
+        # due to tricky Python semantics. The order matters.
+        cur.next = cur = next
+
+
+def _finalize_choice(node):
+    # Finalizes a choice, marking each symbol whose menu node has the choice as
+    # the parent as a choice symbol, and automatically determining types if not
+    # specified.
+
+    choice = node.item
+
+    cur = node.list
+    while cur:
+        if cur.item.__class__ is Symbol:
+            cur.item.choice = choice
+            choice.syms.append(cur.item)
+        cur = cur.next
+
+    # If no type is specified for the choice, its type is that of
+    # the first choice item with a specified type
+    if not choice.orig_type:
+        for item in choice.syms:
+            if item.orig_type:
+                choice.orig_type = item.orig_type
+                break
+
+    # Each choice item of UNKNOWN type gets the type of the choice
+    for sym in choice.syms:
+        if not sym.orig_type:
+            sym.orig_type = choice.orig_type
+
+
+def _check_dep_loop_sym(sym, ignore_choice):
+    # Detects dependency loops using depth-first search on the dependency graph
+    # (which is calculated earlier in Kconfig._build_dep()).
+    #
+    # Algorithm:
+    #
+    #  1. Symbols/choices start out with _visited = 0, meaning unvisited.
+    #
+    #  2. When a symbol/choice is first visited, _visited is set to 1, meaning
+    #     "visited, potentially part of a dependency loop". The recursive
+    #     search then continues from the symbol/choice.
+    #
+    #  3. If we run into a symbol/choice X with _visited already set to 1,
+    #     there's a dependency loop. The loop is found on the call stack by
+    #     recording symbols while returning ("on the way back") until X is seen
+    #     again.
+    #
+    #  4. Once a symbol/choice and all its dependencies (or dependents in this
+    #     case) have been checked recursively without detecting any loops, its
+    #     _visited is set to 2, meaning "visited, not part of a dependency
+    #     loop".
+    #
+    #     This saves work if we run into the symbol/choice again in later calls
+    #     to _check_dep_loop_sym(). We just return immediately.
+    #
+    # Choices complicate things, as every choice symbol depends on every other
+    # choice symbol in a sense. When a choice is "entered" via a choice symbol
+    # X, we visit all choice symbols from the choice except X, and prevent
+    # immediately revisiting the choice with a flag (ignore_choice).
+    #
+    # Maybe there's a better way to handle this (different flags or the
+    # like...)
+
+    if not sym._visited:
+        # sym._visited == 0, unvisited
+
+        sym._visited = 1
+
+        for dep in sym._dependents:
+            # Choices show up in Symbol._dependents when the choice has the
+            # symbol in a 'prompt' or 'default' condition (e.g.
+            # 'default ... if SYM').
+            #
+            # Since we aren't entering the choice via a choice symbol, all
+            # choice symbols need to be checked, hence the None.
+            loop = _check_dep_loop_choice(dep, None) \
+                   if dep.__class__ is Choice \
+                   else _check_dep_loop_sym(dep, False)
+
+            if loop:
+                # Dependency loop found
+                return _found_dep_loop(loop, sym)
+
+        if sym.choice and not ignore_choice:
+            loop = _check_dep_loop_choice(sym.choice, sym)
+            if loop:
+                # Dependency loop found
+                return _found_dep_loop(loop, sym)
+
+        # The symbol is not part of a dependency loop
+        sym._visited = 2
+
+        # No dependency loop found
+        return None
+
+    if sym._visited == 2:
+        # The symbol was checked earlier and is already known to not be part of
+        # a dependency loop
+        return None
+
+    # sym._visited == 1, found a dependency loop. Return the symbol as the
+    # first element in it.
+    return (sym,)
+
+
+def _check_dep_loop_choice(choice, skip):
+    if not choice._visited:
+        # choice._visited == 0, unvisited
+
+        choice._visited = 1
+
+        # Check for loops involving choice symbols. If we came here via a
+        # choice symbol, skip that one, as we'd get a false positive
+        # '<sym FOO> -> <choice> -> <sym FOO>' loop otherwise.
+        for sym in choice.syms:
+            if sym is not skip:
+                # Prevent the choice from being immediately re-entered via the
+                # "is a choice symbol" path by passing True
+                loop = _check_dep_loop_sym(sym, True)
+                if loop:
+                    # Dependency loop found
+                    return _found_dep_loop(loop, choice)
+
+        # The choice is not part of a dependency loop
+        choice._visited = 2
+
+        # No dependency loop found
+        return None
+
+    if choice._visited == 2:
+        # The choice was checked earlier and is already known to not be part of
+        # a dependency loop
+        return None
+
+    # choice._visited == 1, found a dependency loop. Return the choice as the
+    # first element in it.
+    return (choice,)
+
+
+def _found_dep_loop(loop, cur):
+    # Called "on the way back" when we know we have a loop
+
+    # Is the symbol/choice 'cur' where the loop started?
+    if cur is not loop[0]:
+        # Nope, it's just a part of the loop
+        return loop + (cur,)
+
+    # Yep, we have the entire loop. Throw an exception that shows it.
+
+    msg = "\nDependency loop\n" \
+            "===============\n\n"
+
+    for item in loop:
+        if item is not loop[0]:
+            msg += "...depends on "
+            if item.__class__ is Symbol and item.choice:
+                msg += "the choice symbol "
+
+        msg += "{}, with definition...\n\n{}\n\n" \
+               .format(_name_and_loc(item), item)
+
+        # Small wart: Since we reuse the already calculated
+        # Symbol/Choice._dependents sets for recursive dependency detection, we
+        # lose information on whether a dependency came from a 'select'/'imply'
+        # condition or e.g. a 'depends on'.
+        #
+        # This might cause selecting symbols to "disappear". For example,
+        # a symbol B having 'select A if C' gives a direct dependency from A to
+        # C, since it corresponds to a reverse dependency of B && C.
+        #
+        # Always print reverse dependencies for symbols that have them to make
+        # sure information isn't lost. I wonder if there's some neat way to
+        # improve this.
+
+        if item.__class__ is Symbol:
+            if item.rev_dep is not item.kconfig.n:
+                msg += "(select-related dependencies: {})\n\n" \
+                       .format(expr_str(item.rev_dep))
+
+            if item.weak_rev_dep is not item.kconfig.n:
+                msg += "(imply-related dependencies: {})\n\n" \
+                       .format(expr_str(item.rev_dep))
+
+    msg += "...depends again on {}".format(_name_and_loc(loop[0]))
+
+    raise KconfigError(msg)
+
+
+def _decoding_error(e, filename, macro_linenr=None):
+    # Gives the filename and context for UnicodeDecodeError's, which are a pain
+    # to debug otherwise. 'e' is the UnicodeDecodeError object.
+    #
+    # If the decoding error is for the output of a $(shell,...) command,
+    # macro_linenr holds the line number where it was run (the exact line
+    # number isn't available for decoding errors in files).
+
+    raise KconfigError(
+        "\n"
+        "Malformed {} in {}\n"
+        "Context: {}\n"
+        "Problematic data: {}\n"
+        "Reason: {}".format(
+            e.encoding,
+            "'{}'".format(filename) if macro_linenr is None else
+                "output from macro at {}:{}".format(filename, macro_linenr),
+            e.object[max(e.start - 40, 0):e.end + 40],
+            e.object[e.start:e.end],
+            e.reason))
+
+
+def _warn_verbose_deprecated(fn_name):
+    sys.stderr.write(
+        "Deprecation warning: {0}()'s 'verbose' argument has no effect. Since "
+        "Kconfiglib 12.0.0, the message is returned from {0}() instead, "
+        "and is always generated. Do e.g. print(kconf.{0}()) if you want to "
+        "want to show a message like \"Loaded configuration '.config'\" on "
+        "stdout. The old API required ugly hacks to reuse messages in "
+        "configuration interfaces.\n".format(fn_name))
+
+
+# Predefined preprocessor functions
+
+
+def _filename_fn(kconf, _):
+    return kconf.filename
+
+
+def _lineno_fn(kconf, _):
+    return str(kconf.linenr)
+
+
+def _info_fn(kconf, _, msg):
+    print("{}:{}: {}".format(kconf.filename, kconf.linenr, msg))
+
+    return ""
+
+
+def _warning_if_fn(kconf, _, cond, msg):
+    if cond == "y":
+        kconf._warn(msg, kconf.filename, kconf.linenr)
+
+    return ""
+
+
+def _error_if_fn(kconf, _, cond, msg):
+    if cond == "y":
+        raise KconfigError("{}:{}: {}".format(
+            kconf.filename, kconf.linenr, msg))
+
+    return ""
+
+
+def _shell_fn(kconf, _, command):
+    # Only import as needed, to save some startup time
+    import subprocess
+
+    stdout, stderr = subprocess.Popen(
+        command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE
+    ).communicate()
+
+    if not _IS_PY2:
+        try:
+            stdout = stdout.decode(kconf._encoding)
+            stderr = stderr.decode(kconf._encoding)
+        except UnicodeDecodeError as e:
+            _decoding_error(e, kconf.filename, kconf.linenr)
+
+    if stderr:
+        kconf._warn("'{}' wrote to stderr: {}".format(
+                        command, "\n".join(stderr.splitlines())),
+                    kconf.filename, kconf.linenr)
+
+    # Universal newlines with splitlines() (to prevent e.g. stray \r's in
+    # command output on Windows), trailing newline removal, and
+    # newline-to-space conversion.
+    #
+    # On Python 3 versions before 3.6, it's not possible to specify the
+    # encoding when passing universal_newlines=True to Popen() (the 'encoding'
+    # parameter was added in 3.6), so we do this manual version instead.
+    return "\n".join(stdout.splitlines()).rstrip("\n").replace("\n", " ")
 
 #
-# Internal global constants
+# Global constants
 #
 
-# Tokens
-(T_AND, T_OR, T_NOT,
- T_OPEN_PAREN, T_CLOSE_PAREN,
- T_EQUAL, T_UNEQUAL,
- T_MAINMENU, T_MENU, T_ENDMENU,
- T_SOURCE, T_CHOICE, T_ENDCHOICE,
- T_COMMENT, T_CONFIG, T_MENUCONFIG,
- T_HELP, T_IF, T_ENDIF, T_DEPENDS, T_ON,
- T_OPTIONAL, T_PROMPT, T_DEFAULT,
- T_BOOL, T_TRISTATE, T_HEX, T_INT, T_STRING,
- T_DEF_BOOL, T_DEF_TRISTATE,
- T_SELECT, T_IMPLY, T_RANGE, T_OPTION, T_ALLNOCONFIG_Y, T_ENV,
- T_DEFCONFIG_LIST, T_MODULES, T_VISIBLE) = range(40)
+TRI_TO_STR = {
+    0: "n",
+    1: "m",
+    2: "y",
+}
 
-# The leading underscore before the function assignments below prevent pydoc
-# from listing them. The constants could be hidden too, but they're fairly
-# obviously internal anyway, so don't bother spamming the code.
+STR_TO_TRI = {
+    "n": 0,
+    "m": 1,
+    "y": 2,
+}
 
-# Keyword to token map. Note that the get() method is assigned directly as a
-# small optimization.
-_get_keyword = \
-  {"mainmenu": T_MAINMENU, "menu": T_MENU, "endmenu": T_ENDMENU,
-   "endif": T_ENDIF, "endchoice": T_ENDCHOICE, "source": T_SOURCE,
-   "choice": T_CHOICE, "config": T_CONFIG, "comment": T_COMMENT,
-   "menuconfig": T_MENUCONFIG, "help": T_HELP, "if": T_IF,
-   "depends": T_DEPENDS, "on": T_ON, "optional": T_OPTIONAL,
-   "prompt": T_PROMPT, "default": T_DEFAULT, "bool": T_BOOL, "boolean": T_BOOL,
-   "tristate": T_TRISTATE, "int": T_INT, "hex": T_HEX, "def_bool": T_DEF_BOOL,
-   "def_tristate": T_DEF_TRISTATE, "string": T_STRING, "select": T_SELECT,
-   "imply" : T_IMPLY, "range": T_RANGE, "option": T_OPTION,
-   "allnoconfig_y": T_ALLNOCONFIG_Y, "env": T_ENV,
-   "defconfig_list": T_DEFCONFIG_LIST, "modules": T_MODULES,
-   "visible": T_VISIBLE}.get
+# Constant representing that there's no cached choice selection. This is
+# distinct from a cached None (no selection). Any object that's not None or a
+# Symbol will do. We test this with 'is'.
+_NO_CACHED_SELECTION = 0
 
-# Strings to use for True and False
-BOOL_STR = {False: "false", True: "true"}
+# Are we running on Python 2?
+_IS_PY2 = sys.version_info[0] < 3
 
-# Tokens after which identifier-like lexemes are treated as strings. T_CHOICE
-# is included to avoid symbols being registered for named choices.
-STRING_LEX = frozenset((T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING, T_CHOICE,
-                        T_PROMPT, T_MENU, T_COMMENT, T_SOURCE, T_MAINMENU))
+try:
+    _UNAME_RELEASE = os.uname()[2]
+except AttributeError:
+    # Only import as needed, to save some startup time
+    import platform
+    _UNAME_RELEASE = platform.uname()[2]
 
-# Matches the initial token on a line; see _tokenize(). Also eats trailing
-# whitespace as an optimization.
-_initial_token_re_match = re.compile(r"[^\w]*(\w+)\s*").match
+# The token and type constants below are safe to test with 'is', which is a bit
+# faster (~30% faster on my machine, and a few % faster for total parsing
+# time), even without assuming Python's small integer optimization (which
+# caches small integer objects). The constants end up pointing to unique
+# integer objects, and since we consistently refer to them via the names below,
+# we always get the same object.
+#
+# Client code should use == though.
 
-# Matches an identifier/keyword optionally preceded by whitespace. Also eats
-# trailing whitespace as an optimization.
-_id_keyword_re_match = re.compile(r"\s*([\w./-]+)\s*").match
+# Tokens, with values 1, 2, ... . Avoiding 0 simplifies some checks by making
+# all tokens except empty strings truthy.
+(
+    _T_ALLNOCONFIG_Y,
+    _T_AND,
+    _T_BOOL,
+    _T_CHOICE,
+    _T_CLOSE_PAREN,
+    _T_COMMENT,
+    _T_CONFIG,
+    _T_DEFAULT,
+    _T_DEFCONFIG_LIST,
+    _T_DEF_BOOL,
+    _T_DEF_HEX,
+    _T_DEF_INT,
+    _T_DEF_STRING,
+    _T_DEF_TRISTATE,
+    _T_DEPENDS,
+    _T_ENDCHOICE,
+    _T_ENDIF,
+    _T_ENDMENU,
+    _T_ENV,
+    _T_EQUAL,
+    _T_GREATER,
+    _T_GREATER_EQUAL,
+    _T_HELP,
+    _T_HEX,
+    _T_IF,
+    _T_IMPLY,
+    _T_INT,
+    _T_LESS,
+    _T_LESS_EQUAL,
+    _T_MAINMENU,
+    _T_MENU,
+    _T_MENUCONFIG,
+    _T_MODULES,
+    _T_NOT,
+    _T_ON,
+    _T_OPEN_PAREN,
+    _T_OPTION,
+    _T_OPTIONAL,
+    _T_OR,
+    _T_ORSOURCE,
+    _T_OSOURCE,
+    _T_PROMPT,
+    _T_RANGE,
+    _T_RSOURCE,
+    _T_SELECT,
+    _T_SOURCE,
+    _T_STRING,
+    _T_TRISTATE,
+    _T_UNEQUAL,
+    _T_VISIBLE,
+) = range(1, 51)
 
-# Regular expression for finding $-references to symbols in strings
-_sym_ref_re_search = re.compile(r"\$[A-Za-z0-9_]+").search
+# Keyword to token map, with the get() method assigned directly as a small
+# optimization
+_get_keyword = {
+    "---help---":     _T_HELP,
+    "allnoconfig_y":  _T_ALLNOCONFIG_Y,
+    "bool":           _T_BOOL,
+    "boolean":        _T_BOOL,
+    "choice":         _T_CHOICE,
+    "comment":        _T_COMMENT,
+    "config":         _T_CONFIG,
+    "def_bool":       _T_DEF_BOOL,
+    "def_hex":        _T_DEF_HEX,
+    "def_int":        _T_DEF_INT,
+    "def_string":     _T_DEF_STRING,
+    "def_tristate":   _T_DEF_TRISTATE,
+    "default":        _T_DEFAULT,
+    "defconfig_list": _T_DEFCONFIG_LIST,
+    "depends":        _T_DEPENDS,
+    "endchoice":      _T_ENDCHOICE,
+    "endif":          _T_ENDIF,
+    "endmenu":        _T_ENDMENU,
+    "env":            _T_ENV,
+    "grsource":       _T_ORSOURCE,  # Backwards compatibility
+    "gsource":        _T_OSOURCE,   # Backwards compatibility
+    "help":           _T_HELP,
+    "hex":            _T_HEX,
+    "if":             _T_IF,
+    "imply":          _T_IMPLY,
+    "int":            _T_INT,
+    "mainmenu":       _T_MAINMENU,
+    "menu":           _T_MENU,
+    "menuconfig":     _T_MENUCONFIG,
+    "modules":        _T_MODULES,
+    "on":             _T_ON,
+    "option":         _T_OPTION,
+    "optional":       _T_OPTIONAL,
+    "orsource":       _T_ORSOURCE,
+    "osource":        _T_OSOURCE,
+    "prompt":         _T_PROMPT,
+    "range":          _T_RANGE,
+    "rsource":        _T_RSOURCE,
+    "select":         _T_SELECT,
+    "source":         _T_SOURCE,
+    "string":         _T_STRING,
+    "tristate":       _T_TRISTATE,
+    "visible":        _T_VISIBLE,
+}.get
 
-# Integers representing symbol types
-UNKNOWN, BOOL, TRISTATE, STRING, HEX, INT = range(6)
+# The constants below match the value of the corresponding tokens to remove the
+# need for conversion
 
-# Strings to use for types
-TYPENAME = {UNKNOWN: "unknown", BOOL: "bool", TRISTATE: "tristate",
-            STRING: "string", HEX: "hex", INT: "int"}
+# Node types
+MENU    = _T_MENU
+COMMENT = _T_COMMENT
 
-# Token to type mapping
-TOKEN_TO_TYPE = {T_BOOL: BOOL, T_TRISTATE: TRISTATE, T_STRING: STRING,
-                 T_INT: INT, T_HEX: HEX}
+# Expression types
+AND           = _T_AND
+OR            = _T_OR
+NOT           = _T_NOT
+EQUAL         = _T_EQUAL
+UNEQUAL       = _T_UNEQUAL
+LESS          = _T_LESS
+LESS_EQUAL    = _T_LESS_EQUAL
+GREATER       = _T_GREATER
+GREATER_EQUAL = _T_GREATER_EQUAL
 
-# Default values for symbols of different types (the value the symbol gets if
-# it is not assigned a user value and none of its 'default' clauses kick in)
-DEFAULT_VALUE = {BOOL: "n", TRISTATE: "n", STRING: "", INT: "", HEX: ""}
+REL_TO_STR = {
+    EQUAL:         "=",
+    UNEQUAL:       "!=",
+    LESS:          "<",
+    LESS_EQUAL:    "<=",
+    GREATER:       ">",
+    GREATER_EQUAL: ">=",
+}
 
-# Indicates that no item is selected in a choice statement
-NO_SELECTION = 0
+# Symbol/choice types. UNKNOWN is 0 (falsy) to simplify some checks.
+# Client code shouldn't rely on it though, as it was non-zero in
+# older versions.
+UNKNOWN  = 0
+BOOL     = _T_BOOL
+TRISTATE = _T_TRISTATE
+STRING   = _T_STRING
+INT      = _T_INT
+HEX      = _T_HEX
 
-# Integers representing expression types
-AND, OR, NOT, EQUAL, UNEQUAL = range(5)
+TYPE_TO_STR = {
+    UNKNOWN:  "unknown",
+    BOOL:     "bool",
+    TRISTATE: "tristate",
+    STRING:   "string",
+    INT:      "int",
+    HEX:      "hex",
+}
 
-# Map from tristate values to integers
-TRI_TO_INT = {"n": 0, "m": 1, "y": 2}
+# Used in comparisons. 0 means the base is inferred from the format of the
+# string.
+_TYPE_TO_BASE = {
+    HEX:      16,
+    INT:      10,
+    STRING:   0,
+    UNKNOWN:  0,
+}
 
-# Printing-related stuff
+# def_bool -> BOOL, etc.
+_DEF_TOKEN_TO_TYPE = {
+    _T_DEF_BOOL:     BOOL,
+    _T_DEF_HEX:      HEX,
+    _T_DEF_INT:      INT,
+    _T_DEF_STRING:   STRING,
+    _T_DEF_TRISTATE: TRISTATE,
+}
 
-OP_TO_STR = {AND: " && ", OR: " || ", EQUAL: " = ", UNEQUAL: " != "}
-PRECEDENCE = {OR: 0, AND: 1, NOT: 2}
+# Tokens after which strings are expected. This is used to tell strings from
+# constant symbol references during tokenization, both of which are enclosed in
+# quotes.
+#
+# Identifier-like lexemes ("missing quotes") are also treated as strings after
+# these tokens. _T_CHOICE is included to avoid symbols being registered for
+# named choices.
+_STRING_LEX = frozenset({
+    _T_BOOL,
+    _T_CHOICE,
+    _T_COMMENT,
+    _T_HEX,
+    _T_INT,
+    _T_MAINMENU,
+    _T_MENU,
+    _T_ORSOURCE,
+    _T_OSOURCE,
+    _T_PROMPT,
+    _T_RSOURCE,
+    _T_SOURCE,
+    _T_STRING,
+    _T_TRISTATE,
+})
+
+# Various sets for quick membership tests. Gives a single global lookup and
+# avoids creating temporary dicts/tuples.
+
+_TYPE_TOKENS = frozenset({
+    _T_BOOL,
+    _T_TRISTATE,
+    _T_INT,
+    _T_HEX,
+    _T_STRING,
+})
+
+_SOURCE_TOKENS = frozenset({
+    _T_SOURCE,
+    _T_RSOURCE,
+    _T_OSOURCE,
+    _T_ORSOURCE,
+})
+
+_REL_SOURCE_TOKENS = frozenset({
+    _T_RSOURCE,
+    _T_ORSOURCE,
+})
+
+# Obligatory (non-optional) sources
+_OBL_SOURCE_TOKENS = frozenset({
+    _T_SOURCE,
+    _T_RSOURCE,
+})
+
+_BOOL_TRISTATE = frozenset({
+    BOOL,
+    TRISTATE,
+})
+
+_BOOL_TRISTATE_UNKNOWN = frozenset({
+    BOOL,
+    TRISTATE,
+    UNKNOWN,
+})
+
+_INT_HEX = frozenset({
+    INT,
+    HEX,
+})
+
+_SYMBOL_CHOICE = frozenset({
+    Symbol,
+    Choice,
+})
+
+_MENU_COMMENT = frozenset({
+    MENU,
+    COMMENT,
+})
+
+_EQUAL_UNEQUAL = frozenset({
+    EQUAL,
+    UNEQUAL,
+})
+
+_RELATIONS = frozenset({
+    EQUAL,
+    UNEQUAL,
+    LESS,
+    LESS_EQUAL,
+    GREATER,
+    GREATER_EQUAL,
+})
+
+# Helper functions for getting compiled regular expressions, with the needed
+# matching function returned directly as a small optimization.
+#
+# Use ASCII regex matching on Python 3. It's already the default on Python 2.
+
+
+def _re_match(regex):
+    return re.compile(regex, 0 if _IS_PY2 else re.ASCII).match
+
+
+def _re_search(regex):
+    return re.compile(regex, 0 if _IS_PY2 else re.ASCII).search
+
+
+# Various regular expressions used during parsing
+
+# The initial token on a line. Also eats leading and trailing whitespace, so
+# that we can jump straight to the next token (or to the end of the line if
+# there is only one token).
+#
+# This regex will also fail to match for empty lines and comment lines.
+#
+# '$' is included to detect preprocessor variable assignments with macro
+# expansions in the left-hand side.
+_command_match = _re_match(r"\s*([A-Za-z0-9_$-]+)\s*")
+
+# An identifier/keyword after the first token. Also eats trailing whitespace.
+# '$' is included to detect identifiers containing macro expansions.
+_id_keyword_match = _re_match(r"([A-Za-z0-9_$/.-]+)\s*")
+
+# A fragment in the left-hand side of a preprocessor variable assignment. These
+# are the portions between macro expansions ($(foo)). Macros are supported in
+# the LHS (variable name).
+_assignment_lhs_fragment_match = _re_match("[A-Za-z0-9_-]*")
+
+# The assignment operator and value (right-hand side) in a preprocessor
+# variable assignment
+_assignment_rhs_match = _re_match(r"\s*(=|:=|\+=)\s*(.*)")
+
+# Special characters/strings while expanding a macro (')', ',', and '$(')
+_macro_special_search = _re_search(r"\)|,|\$\(")
+
+# Special characters/strings while expanding a string (quotes, '\', and '$(')
+_string_special_search = _re_search(r'"|\'|\\|\$\(')
+
+# Special characters/strings while expanding a symbol name. Also includes
+# end-of-line, in case the macro is the last thing on the line.
+_name_special_search = _re_search(r'[^A-Za-z0-9_$/.-]|\$\(|$')
+
+# A valid right-hand side for an assignment to a string symbol in a .config
+# file, including escaped characters. Extracts the contents.
+_conf_string_match = _re_match(r'"((?:[^\\"]|\\.)*)"')
diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index 9fd2bd30ef..4ff0bffaef 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -118,12 +118,12 @@ class KconfigScanner:
     }
 
     def __init__(self):
-        """Scan all the Kconfig files and create a Config object."""
+        """Scan all the Kconfig files and create a Kconfig object."""
         # Define environment variables referenced from Kconfig
         os.environ['srctree'] = os.getcwd()
         os.environ['UBOOTVERSION'] = 'dummy'
         os.environ['KCONFIG_OBJDIR'] = ''
-        self._conf = kconfiglib.Config(print_warnings=False)
+        self._conf = kconfiglib.Kconfig(warn=False)
 
     def __del__(self):
         """Delete a leftover temporary file before exit.
@@ -174,7 +174,7 @@ class KconfigScanner:
         # Get the value of CONFIG_SYS_ARCH, CONFIG_SYS_CPU, ... etc.
         # Set '-' if the value is empty.
         for key, symbol in list(self._SYMBOL_TABLE.items()):
-            value = self._conf.get_symbol(symbol).get_value()
+            value = self._conf.syms.get(symbol).str_value
             if value:
                 params[key] = value
             else:
diff --git a/tools/moveconfig.py b/tools/moveconfig.py
index 0bbc7c1991..b99417e9d6 100755
--- a/tools/moveconfig.py
+++ b/tools/moveconfig.py
@@ -851,7 +851,7 @@ class KconfigScanner:
         os.environ['srctree'] = os.getcwd()
         os.environ['UBOOTVERSION'] = 'dummy'
         os.environ['KCONFIG_OBJDIR'] = ''
-        self.conf = kconfiglib.Config()
+        self.conf = kconfiglib.Kconfig()
 
 
 class KconfigParser:
@@ -1525,7 +1525,7 @@ def find_kconfig_rules(kconf, config, imply_config):
     """Check whether a config has a 'select' or 'imply' keyword
 
     Args:
-        kconf: Kconfig.Config object
+        kconf: Kconfiglib.Kconfig object
         config: Name of config to check (without CONFIG_ prefix)
         imply_config: Implying config (without CONFIG_ prefix) which may or
             may not have an 'imply' for 'config')
@@ -1533,7 +1533,7 @@ def find_kconfig_rules(kconf, config, imply_config):
     Returns:
         Symbol object for 'config' if found, else None
     """
-    sym = kconf.get_symbol(imply_config)
+    sym = kconf.syms.get(imply_config)
     if sym:
         for sel in sym.get_selected_symbols() | sym.get_implied_symbols():
             if sel.get_name() == config:
@@ -1547,7 +1547,7 @@ def check_imply_rule(kconf, config, imply_config):
     to add an 'imply' for 'config' to that part of the Kconfig.
 
     Args:
-        kconf: Kconfig.Config object
+        kconf: Kconfiglib.Kconfig object
         config: Name of config to check (without CONFIG_ prefix)
         imply_config: Implying config (without CONFIG_ prefix) which may or
             may not have an 'imply' for 'config')
@@ -1558,7 +1558,7 @@ def check_imply_rule(kconf, config, imply_config):
             line number within the Kconfig file, or 0 if none
             message indicating the result
     """
-    sym = kconf.get_symbol(imply_config)
+    sym = kconf.syms.get(imply_config)
     if not sym:
         return 'cannot find sym'
     locs = sym.get_def_locations()
@@ -1784,7 +1784,7 @@ def do_imply_config(config_list, add_imply, imply_flags, skip_added,
                         if skip_added:
                             show = False
                 else:
-                    sym = kconf.get_symbol(iconfig[CONFIG_LEN:])
+                    sym = kconf.syms.get(iconfig[CONFIG_LEN:])
                     fname = ''
                     if sym:
                         locs = sym.get_def_locations()

From aae62584a6a25b5a33f3218fac87ee74362f5bce Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Mon, 7 Oct 2019 17:17:36 -0400
Subject: [PATCH 4/7] buildman: Perform tests in a temporary directory

We may not always be able to write to the default output directory so
have a temporary directory for our output be created.

Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Stephen Warren <swarren@wwwdotorg.org>
Suggested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
---
 tools/buildman/func_test.py | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/tools/buildman/func_test.py b/tools/buildman/func_test.py
index 119d02cbb2..f90b8ea7f5 100644
--- a/tools/buildman/func_test.py
+++ b/tools/buildman/func_test.py
@@ -175,6 +175,7 @@ class TestFunctional(unittest.TestCase):
     """
     def setUp(self):
         self._base_dir = tempfile.mkdtemp()
+        self._output_dir = tempfile.mkdtemp()
         self._git_dir = os.path.join(self._base_dir, 'src')
         self._buildman_pathname = sys.argv[0]
         self._buildman_dir = os.path.dirname(os.path.realpath(sys.argv[0]))
@@ -207,6 +208,7 @@ class TestFunctional(unittest.TestCase):
 
     def tearDown(self):
         shutil.rmtree(self._base_dir)
+        shutil.rmtree(self._output_dir)
 
     def setupToolchains(self):
         self._toolchains = toolchain.Toolchains()
@@ -421,7 +423,7 @@ class TestFunctional(unittest.TestCase):
     def testCurrentSource(self):
         """Very simple test to invoke buildman on the current source"""
         self.setupToolchains();
-        self._RunControl()
+        self._RunControl('-o', self._output_dir)
         lines = terminal.GetPrintTestLines()
         self.assertIn('Building current source for %d boards' % len(boards),
                       lines[0].text)
@@ -434,7 +436,7 @@ class TestFunctional(unittest.TestCase):
     def testBadToolchain(self):
         """Test that missing toolchains are detected"""
         self.setupToolchains();
-        ret_code = self._RunControl('-b', TEST_BRANCH)
+        ret_code = self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir)
         lines = terminal.GetPrintTestLines()
 
         # Buildman always builds the upstream commit as well
@@ -458,13 +460,13 @@ class TestFunctional(unittest.TestCase):
 
     def testBranch(self):
         """Test building a branch with all toolchains present"""
-        self._RunControl('-b', TEST_BRANCH)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir)
         self.assertEqual(self._builder.count, self._total_builds)
         self.assertEqual(self._builder.fail, 0)
 
     def testCount(self):
         """Test building a specific number of commitst"""
-        self._RunControl('-b', TEST_BRANCH, '-c2')
+        self._RunControl('-b', TEST_BRANCH, '-c2', '-o', self._output_dir)
         self.assertEqual(self._builder.count, 2 * len(boards))
         self.assertEqual(self._builder.fail, 0)
         # Each board has a mrproper, config, and then one make per commit
@@ -472,34 +474,34 @@ class TestFunctional(unittest.TestCase):
 
     def testIncremental(self):
         """Test building a branch twice - the second time should do nothing"""
-        self._RunControl('-b', TEST_BRANCH)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir)
 
         # Each board has a mrproper, config, and then one make per commit
         self.assertEqual(self._make_calls, len(boards) * (self._commits + 2))
         self._make_calls = 0
-        self._RunControl('-b', TEST_BRANCH, clean_dir=False)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir, clean_dir=False)
         self.assertEqual(self._make_calls, 0)
         self.assertEqual(self._builder.count, self._total_builds)
         self.assertEqual(self._builder.fail, 0)
 
     def testForceBuild(self):
         """The -f flag should force a rebuild"""
-        self._RunControl('-b', TEST_BRANCH)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir)
         self._make_calls = 0
-        self._RunControl('-b', TEST_BRANCH, '-f', clean_dir=False)
+        self._RunControl('-b', TEST_BRANCH, '-f', '-o', self._output_dir, clean_dir=False)
         # Each board has a mrproper, config, and then one make per commit
         self.assertEqual(self._make_calls, len(boards) * (self._commits + 2))
 
     def testForceReconfigure(self):
         """The -f flag should force a rebuild"""
-        self._RunControl('-b', TEST_BRANCH, '-C')
+        self._RunControl('-b', TEST_BRANCH, '-C', '-o', self._output_dir)
         # Each commit has a mrproper, config and make
         self.assertEqual(self._make_calls, len(boards) * self._commits * 3)
 
     def testErrors(self):
         """Test handling of build errors"""
         self._error['board2', 1] = 'fred\n'
-        self._RunControl('-b', TEST_BRANCH)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir)
         self.assertEqual(self._builder.count, self._total_builds)
         self.assertEqual(self._builder.fail, 1)
 
@@ -507,13 +509,13 @@ class TestFunctional(unittest.TestCase):
         # not be rebuilt
         del self._error['board2', 1]
         self._make_calls = 0
-        self._RunControl('-b', TEST_BRANCH, clean_dir=False)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir, clean_dir=False)
         self.assertEqual(self._builder.count, self._total_builds)
         self.assertEqual(self._make_calls, 0)
         self.assertEqual(self._builder.fail, 1)
 
         # Now use the -F flag to force rebuild of the bad commit
-        self._RunControl('-b', TEST_BRANCH, '-F', clean_dir=False)
+        self._RunControl('-b', TEST_BRANCH, '-o', self._output_dir, '-F', clean_dir=False)
         self.assertEqual(self._builder.count, self._total_builds)
         self.assertEqual(self._builder.fail, 0)
         self.assertEqual(self._make_calls, 3)

From db7b8602816ed6230d21ae055be5fda55549fb50 Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Fri, 4 Oct 2019 12:12:53 -0400
Subject: [PATCH 5/7] gitlab-ci: Have buildman use /tmp for output

When running as another user we might not be able to use '..' for
certain directories and this is the default for buildman.  Specify an
output directory instead.

Signed-off-by: Tom Rini <trini@konsulko.com>
---
 .gitlab-ci.yml | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0c4343468d..a37e0e8066 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -36,9 +36,9 @@ stages:
     # use clang only do one configuration.
     - if [[ "${BUILDMAN}" != "" ]]; then
         ret=0;
-        tools/buildman/buildman -P -E ${BUILDMAN} ${OVERRIDE}|| ret=$?;
+        tools/buildman/buildman -o /tmp -P -E ${BUILDMAN} ${OVERRIDE}|| ret=$?;
         if [[ $ret -ne 0 && $ret -ne 129 ]]; then
-          tools/buildman/buildman -sdeP ${BUILDMAN};
+          tools/buildman/buildman -o /tmp -sdeP ${BUILDMAN};
           exit $ret;
         fi;
       fi
@@ -46,7 +46,7 @@ stages:
     # never prevent any test from running. That way, we can always pass
     # "-k something" even when $TEST_PY_TEST_SPEC doesnt need a custom
     # value.
-    - export UBOOT_TRAVIS_BUILD_DIR=`cd .. && pwd`/.bm-work/${TEST_PY_BD};
+    - export UBOOT_TRAVIS_BUILD_DIR=/tmp/.bm-work/${TEST_PY_BD};
       export PATH=/opt/qemu/bin:/tmp/uboot-test-hooks/bin:/usr/bin:/bin;
       export PYTHONPATH=/tmp/uboot-test-hooks/py/travis-ci;
       if [[ "${TEST_PY_BD}" != "" ]]; then
@@ -64,9 +64,9 @@ build all 32bit ARM platforms:
   stage: world build
   script:
     - ret=0;
-     ./tools/buildman/buildman -P -E arm -x aarch64 || ret=$?;
+     ./tools/buildman/buildman -o /tmp -P -E arm -x aarch64 || ret=$?;
      if [[ $ret -ne 0 && $ret -ne 129 ]]; then
-       ./tools/buildman/buildman -sdeP;
+       ./tools/buildman/buildman -o /tmp -sdeP;
        exit $ret;
      fi;
 
@@ -78,9 +78,9 @@ build all 64bit ARM platforms:
     - . /tmp/venv/bin/activate
     - pip install pyelftools
     - ret=0;
-     ./tools/buildman/buildman -P -E aarch64 || ret=$?;
+     ./tools/buildman/buildman -o /tmp -P -E aarch64 || ret=$?;
      if [[ $ret -ne 0 && $ret -ne 129 ]]; then
-       ./tools/buildman/buildman -sdeP;
+       ./tools/buildman/buildman -o /tmp -sdeP;
        exit $ret;
      fi;
 
@@ -89,9 +89,9 @@ build all PowerPC platforms:
   stage: world build
   script:
     - ret=0;
-     ./tools/buildman/buildman -P -E powerpc || ret=$?;
+     ./tools/buildman/buildman -o /tmp -P -E powerpc || ret=$?;
      if [[ $ret -ne 0 && $ret -ne 129 ]]; then
-       ./tools/buildman/buildman -sdeP;
+       ./tools/buildman/buildman -o /tmp -sdeP;
        exit $ret;
      fi;
 
@@ -100,9 +100,9 @@ build all other platforms:
   stage: world build
   script:
     - ret=0;
-     ./tools/buildman/buildman -P -E -x arm,powerpc || ret=$?;
+     ./tools/buildman/buildman -o /tmp -P -E -x arm,powerpc || ret=$?;
      if [[ $ret -ne 0 && $ret -ne 129 ]]; then
-       ./tools/buildman/buildman -sdeP;
+       ./tools/buildman/buildman -o /tmp -sdeP;
        exit $ret;
      fi;
 
@@ -162,10 +162,10 @@ Run binman, buildman, dtoc and patman testsuites:
       virtualenv /tmp/venv;
       . /tmp/venv/bin/activate;
       pip install pyelftools;
-      export UBOOT_TRAVIS_BUILD_DIR=`cd .. && pwd`/.bm-work/sandbox_spl;
+      export UBOOT_TRAVIS_BUILD_DIR=/tmp/.bm-work/sandbox_spl;
       export PYTHONPATH="${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc/pylibfdt";
       export PATH="${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc:${PATH}";
-      ./tools/buildman/buildman -P sandbox_spl;
+      ./tools/buildman/buildman -o /tmp -P sandbox_spl;
       ./tools/binman/binman --toolpath ${UBOOT_TRAVIS_BUILD_DIR}/tools test;
       ./tools/buildman/buildman -t;
       ./tools/dtoc/dtoc -t;

From 28a51234173ca62b49518053e15bd6d9e88b10cf Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Fri, 4 Oct 2019 12:12:54 -0400
Subject: [PATCH 6/7] gitlab-ci: Switch to Ubuntu 18.04 image

In order to run all filesystem tests we need to have newer ext4 tools,
move up to Ubuntu 18.04 'bionic' for our base.  We need to change
slightly how we invoke the provided grub-mkimage.  This will also make
future python3 work easier.

Signed-off-by: Tom Rini <trini@konsulko.com>
---
 .gitlab-ci.yml | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a37e0e8066..967abed9f2 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -2,7 +2,7 @@
 
 # Grab our configured image.  The source for this is found at:
 # https://gitlab.denx.de/u-boot/gitlab-ci-runner
-image: trini/u-boot-gitlab-ci-runner:xenial-20190720-02Aug2019
+image: trini/u-boot-gitlab-ci-runner:bionic-20190912.1-03Oct2019
 
 # We run some tests in different order, to catch some failures quicker.
 stages:
@@ -22,8 +22,9 @@ stages:
     - . /tmp/venv/bin/activate
     - pip install pytest==2.8.7
     - pip install python-subunit
-    - grub-mkimage -o ~/grub_x86.efi -O i386-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
-    - grub-mkimage -o ~/grub_x64.efi -O x86_64-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
+    - pip install coverage
+    - grub-mkimage --prefix="" -o ~/grub_x86.efi -O i386-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
+    - grub-mkimage --prefix="" -o ~/grub_x64.efi -O x86_64-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
     - mkdir ~/grub2-arm
     - ( cd ~/grub2-arm; wget -O - http://download.opensuse.org/ports/armv7hl/distribution/leap/42.2/repo/oss/suse/armv7hl/grub2-arm-efi-2.02~beta2-87.1.armv7hl.rpm | rpm2cpio | cpio -di )
     - mkdir ~/grub2-arm64

From 8b13e9bf1df2397ae7a814c80d669772f7133b15 Mon Sep 17 00:00:00 2001
From: Tom Rini <trini@konsulko.com>
Date: Tue, 8 Oct 2019 08:39:26 -0400
Subject: [PATCH 7/7] travis.yml: Switch to bionic for the host distribution

To match what we're doing in GitLab, move to 'bionic' for these builds
as well.

Signed-off-by: Tom Rini <trini@konsulko.com>
---
 .travis.yml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index 0ce09e35b7..c48b711659 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,7 @@
 # build U-Boot on Travis CI - https://travis-ci.org/
 
 sudo: required
-dist: xenial
+dist: bionic
 
 language: c
 
@@ -12,7 +12,7 @@ addons:
   apt:
     sources:
     - ubuntu-toolchain-r-test
-    - llvm-toolchain-xenial-7
+    - llvm-toolchain-bionic-7
     packages:
     - cppcheck
     - sloccount
@@ -52,12 +52,13 @@ install:
  - pip install pytest==2.8.7
  - pip install python-subunit
  - pip install pyelftools
- - grub-mkimage -o ~/grub_x86.efi -O i386-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
- - grub-mkimage -o ~/grub_x64.efi -O x86_64-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
+ - grub-mkimage --prefix="" -o ~/grub_x86.efi -O i386-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
+ - grub-mkimage --prefix="" -o ~/grub_x64.efi -O x86_64-efi normal  echo lsefimmap lsefi lsefisystab efinet tftp minicmd
  - mkdir ~/grub2-arm
  - ( cd ~/grub2-arm; wget -O - http://download.opensuse.org/ports/armv7hl/distribution/leap/42.2/repo/oss/suse/armv7hl/grub2-arm-efi-2.02~beta2-87.1.armv7hl.rpm | rpm2cpio | cpio -di )
  - mkdir ~/grub2-arm64
  - ( cd ~/grub2-arm64; wget -O - http://download.opensuse.org/ports/aarch64/distribution/leap/42.2/repo/oss/suse/aarch64/grub2-arm64-efi-2.02~beta2-87.1.aarch64.rpm | rpm2cpio | cpio -di )
+ - wget http://mirrors.kernel.org/ubuntu/pool/main/m/mpfr4/libmpfr4_3.1.4-1_amd64.deb && sudo dpkg -i libmpfr4_3.1.4-1_amd64.deb && rm libmpfr4_3.1.4-1_amd64.deb
 
 env:
   global: