GN only writes files if they've changed

tools/gn/function_write_file_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 "base/file_util.h"
+#include "base/files/file.h"
+#include "base/files/scoped_temp_dir.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/functions.h"
+#include "tools/gn/test_with_scope.h"
+
+namespace {
+
+// Returns true on success, false if write_file signaled an error.
+bool CallWriteFile(Scope* scope,
+                   const std::string& filename,
+                   const Value& data) {
+  Err err;
+
+  std::vector<Value> args;
+  args.push_back(Value(NULL, filename));
+  args.push_back(data);
+
+  FunctionCallNode function_call;
+  Value result = functions::RunWriteFile(scope, &function_call, args, &err);
+  EXPECT_EQ(Value::NONE, result.type());  // Should always return none.
+
+  return !err.has_error();
+}
+
+}  // namespace
+
+TEST(WriteFile, WithData) {
+  TestWithScope setup;
+
+  // Make a real directory for writing the files.
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  setup.build_settings()->SetRootPath(temp_dir.path());
+  setup.build_settings()->SetBuildDir(SourceDir("//out/"));
+
+  Value some_string(NULL, "some string contents");
+
+  // Should refuse to write files outside of the output dir.
+  EXPECT_FALSE(CallWriteFile(setup.scope(), "//in_root.txt", some_string));
+  EXPECT_FALSE(CallWriteFile(setup.scope(), "//other_dir/foo.txt",
+                             some_string));
+
+  // Should be able to write to a new dir inside the out dir.
+  EXPECT_TRUE(CallWriteFile(setup.scope(), "//out/foo.txt", some_string));
+  base::FilePath foo_name = temp_dir.path().Append(FILE_PATH_LITERAL("out"))
+      .Append(FILE_PATH_LITERAL("foo.txt"));
+  std::string result_contents;
+  EXPECT_TRUE(base::ReadFileToString(foo_name, &result_contents));
+  EXPECT_EQ(some_string.string_value(), result_contents);
+
+  // Update the contents with a list of a string and a number.
+  Value some_list(NULL, Value::LIST);
+  some_list.list_value().push_back(Value(NULL, "line 1"));
+  some_list.list_value().push_back(Value(NULL, static_cast<int64>(2)));
+  EXPECT_TRUE(CallWriteFile(setup.scope(), "//out/foo.txt", some_list));
+  EXPECT_TRUE(base::ReadFileToString(foo_name, &result_contents));
+  EXPECT_EQ("line 1\n2\n", result_contents);
+
+  // Test that the file is not rewritten if the contents are not changed.
+  // Start by setting the modified time to something old to avoid clock
+  // resolution issues.
+  base::Time old_time = base::Time::Now() - base::TimeDelta::FromDays(1);
+  base::File foo_file(foo_name,
+                      base::File::FLAG_OPEN |
+                      base::File::FLAG_READ | base::File::FLAG_WRITE);
+  ASSERT_TRUE(foo_file.IsValid());
+  foo_file.SetTimes(old_time, old_time);
+
+  // Read the current time to avoid timer resolution issues when comparing
+  // below.
+  base::File::Info original_info;
+  foo_file.GetInfo(&original_info);
+
+  EXPECT_TRUE(CallWriteFile(setup.scope(), "//out/foo.txt", some_list));
+
+  // Verify that the last modified time is the same as before.
+  base::File::Info new_info;
+  foo_file.GetInfo(&new_info);
+  EXPECT_EQ(original_info.last_modified, new_info.last_modified);
+}