GN: Unconditionally write build.ninja.

tools/gn/ninja_build_writer.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 "tools/gn/ninja_build_writer.h"
 
 #include <stddef.h>
 
 #include <fstream>
 #include <map>
@@ skipping 149 matching lines @@
     Err* err) {
   ScopedTrace trace(TraceItem::TRACE_FILE_WRITE, "build.ninja");
 
   std::stringstream file;
   std::stringstream depfile;
   NinjaBuildWriter gen(build_settings, all_settings, default_toolchain,
                        default_toolchain_targets, file, depfile);
   if (!gen.Run(err))
     return false;
 
+  // Unconditionally write the build.ninja. Ninja's build-out-of-date checking
+  // will re-run GN when any build input is newer than build.ninja, so any time
+  // the build is updated, build.ninja's timestamp needs to updated also, even
+  // if the contents haven't been changed.
   base::FilePath ninja_file_name(build_settings->GetFullPath(
       SourceFile(build_settings->build_dir().value() + "build.ninja")));
+  base::CreateDirectory(ninja_file_name.DirName());
+  std::string ninja_contents = file.str();
+  if (base::WriteFile(ninja_file_name, ninja_contents.data(),
+                      static_cast<int>(ninja_contents.size())) !=
+      static_cast<int>(ninja_contents.size()))
+    return false;
+
+  // Dep file listing build dependencies.
   base::FilePath dep_file_name(build_settings->GetFullPath(
       SourceFile(build_settings->build_dir().value() + "build.ninja.d")));
-  base::CreateDirectory(ninja_file_name.DirName());
-
-  if (!WriteFileIfChanged(ninja_file_name, file.str(), err) ||
-      !WriteFileIfChanged(dep_file_name, depfile.str(), err))
+  std::string dep_contents = depfile.str();
+  if (base::WriteFile(dep_file_name, dep_contents.data(),
+                      static_cast<int>(dep_contents.size())) !=
+      static_cast<int>(dep_contents.size()))
     return false;
 
   return true;
 }
 
 void NinjaBuildWriter::WriteNinjaRules() {
   out_ << "rule gn\n";
   out_ << "  command = " << GetSelfInvocationCommand(build_settings_) << "\n";
   out_ << "  description = Regenerating ninja files\n\n";
 
@@ skipping 203 matching lines @@
   EscapeOptions ninja_escape;
   ninja_escape.mode = ESCAPE_NINJA;
 
   // Escape for special chars Ninja will handle.
   std::string escaped = EscapeString(phony_name, ninja_escape, nullptr);
 
   out_ << "build " << escaped << ": phony ";
   path_output_.WriteFile(out_, target->dependency_output_file());
   out_ << std::endl;
 }