Support private values in GN.

tools/gn/parse_tree_unittest.cc

 // Copyright 2014 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/input_file.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/test_with_scope.h"
 
@@ skipping 30 matching lines @@
   // Define b, accessor should succeed now.
   const int64 kBValue = 42;
   err = Err();
   setup.scope()->GetMutableValue("a", false)->scope_value()->SetValue(
       "b", Value(NULL, kBValue), NULL);
   result = accessor.Execute(setup.scope(), &err);
   EXPECT_FALSE(err.has_error());
   ASSERT_EQ(Value::INTEGER, result.type());
   EXPECT_EQ(kBValue, result.int_value());
 }
+
+TEST(ParseTree, BlockUnusedVars) {
+  TestWithScope setup;
+
+  // Printing both values should be OK.
+  TestParseInput input_all_used(
+      "{\n"
+      "  a = 12\n"
+      "  b = 13\n"
+      "  print(\"$a $b\")\n"
+      "}");
+  EXPECT_FALSE(input_all_used.has_error());
+
+  Err err;
+  input_all_used.parsed()->Execute(setup.scope(), &err);
+  EXPECT_FALSE(err.has_error());
+
+  // Skipping one should throw an unused var error.
+  TestParseInput input_unused(
+      "{\n"
+      "  a = 12\n"
+      "  b = 13\n"
+      "  print(\"$a\")\n"
+      "}");
+  EXPECT_FALSE(input_unused.has_error());
+
+  input_unused.parsed()->Execute(setup.scope(), &err);
+  EXPECT_TRUE(err.has_error());
+}