From 0e0f74b7e3ba30e5f428d16b6ca44f117adde319 Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Wed, 27 Oct 2021 13:05:03 -0700
Subject: [PATCH] infra/common.sh: add shard_should_run()

Detects whether test block should be run in the current test shard.

if shard_should_run; then
 ...
fi

Bug: b/185520507
Change-Id: I408d226651630a01c5e447dbff7d26b73426ce42
---
 infra/common.sh | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/infra/common.sh b/infra/common.sh
index b3686e6c..38c82c84 100644
--- a/infra/common.sh
+++ b/infra/common.sh
@@ -71,3 +71,30 @@ setup_ccache() {
     export PATH="/usr/lib/ccache:${PATH}"
   fi
 }
+
+#######################################
+# Detects whether test block should be run in the current test shard.
+# Globals:
+#   TEST_TOTAL_SHARDS: Valid range: [1, N]. Defaults to 1.
+#   TEST_SHARD_INDEX: Valid range: [0, TEST_TOTAL_SHARDS). Defaults to 0.
+#   libwebp_test_id: current test number; incremented with each call.
+# Arguments:
+#   None
+# Returns:
+#   true if the shard is active
+#   false if the shard is inactive
+#######################################
+shard_should_run() {
+  TEST_TOTAL_SHARDS=${TEST_TOTAL_SHARDS:=1}
+  TEST_SHARD_INDEX=${TEST_SHARD_INDEX:=0}
+  libwebp_test_id=${libwebp_test_id:=-1}
+  : $((libwebp_test_id += 1))
+
+  if [[ "${TEST_SHARD_INDEX}" -lt 0 ||
+    "${TEST_SHARD_INDEX}" -ge "${TEST_TOTAL_SHARDS}" ]]; then
+    log_err "Invalid TEST_SHARD_INDEX (${TEST_SHARD_INDEX})!" \
+      "Expected [0, ${TEST_TOTAL_SHARDS})."
+  fi
+
+  [[ "$((libwebp_test_id % TEST_TOTAL_SHARDS))" -eq "${TEST_SHARD_INDEX}" ]]
+}