Add not_needed function

tools/gn/functions_target_unittest.cc

 // Copyright (c) 2013 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/scheduler.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/test_with_scope.h"
 
 
@@ skipping 19 matching lines @@
   TestParseInput source_set_input(
       "source_set(\"foo\") {\n"
       "  unused = 5\n"
       "}\n");
   ASSERT_FALSE(source_set_input.has_error());
   err = Err();
   source_set_input.parsed()->Execute(setup.scope(), &err);
   ASSERT_TRUE(err.has_error());
 }
 
+// Checks that we find uses of identifiers marked as unused.
+TEST(FunctionsTarget, CheckNotNeeded) {
+  Scheduler scheduler;
+  TestWithScope setup;
+
+  // The target generator needs a place to put the targets or it will fail.
+  Scope::ItemVector item_collector;
+  setup.scope()->set_item_collector(&item_collector);
+
+  // Test a good one first.
+  TestParseInput good_input(
+      "a = {x = 1 y = 2}\n"
+      "not_needed(a, \"*\")\n");
+  ASSERT_FALSE(good_input.has_error());
+  Err err;
+  good_input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_FALSE(err.has_error()) << err.message();
+
+  // Test a varible being used before being declared unused.
+  TestParseInput before_input(
+      "a = {x = 1 y = 2}\n"
+      "b = a.x\n"
+      "not_needed(a, \"*\")\n");
+  ASSERT_FALSE(before_input.has_error());
+  err = Err();
+  before_input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_TRUE(err.has_error());
+
+  // Test a varible being used after being declared unused.
+  TestParseInput after_input(
+      "a = {x = 1 y = 2}\n"
+      "assert_unused(a, \"*\")\n"
+      "assert_unused({b = a.x}, [ \"b\" ])\n");
+  ASSERT_FALSE(after_input.has_error());
+  err = Err();
+  after_input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_TRUE(err.has_error());
+}
+
 // Checks that the defaults applied to a template invoked by target() use
 // the name of the template, rather than the string "target" (which is the
 // name of the actual function being called).
 TEST(FunctionsTarget, TemplateDefaults) {
   Scheduler scheduler;
   TestWithScope setup;
 
   // The target generator needs a place to put the targets or it will fail.
   Scope::ItemVector item_collector;
   setup.scope()->set_item_collector(&item_collector);
@@ skipping 13 matching lines @@
       # Invoke the template with target(). This will fail to execute if the
       # defaults were not set properly, because "default_value" won't exist.
       target("my_templ", "foo") {
         print(default_value)
       })");
   ASSERT_FALSE(good_input.has_error());
   Err err;
   good_input.parsed()->Execute(setup.scope(), &err);
   ASSERT_FALSE(err.has_error()) << err.message();
 }