GN: Mark all variables used when defining a template.

tools/gn/function_template_unittest.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/test_with_scope.h"
+
+// Checks that variables used inside template definitions aren't reported
+// unused if they were declared above the template.
+TEST(FunctionTemplate, MarkUsed) {
+  TestWithScope setup;
+  TestParseInput input(
+      "a = 1\n"  // Unused outside of template.
+      "template(\"templ\") {\n"
+      "  print(a)\n"
+      "}\n");
+  ASSERT_FALSE(input.has_error()) << input.parse_err().message();
+
+  Err err;
+  input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_FALSE(err.has_error()) << err.message();
+
+  // Normally the loader calls CheckForUnusedVars() when it loads a file
+  // since normal blocks don't do this check. To avoid having to make this
+  // test much more complicated, just explicitly do the check to make sure
+  // things are marked properly.
+  setup.scope()->CheckForUnusedVars(&err);
+  EXPECT_FALSE(err.has_error());
+}