GN: Makes GN output deterministic

tools/gn/ninja_toolchain_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_toolchain_writer.h"
 
 #include <fstream>
 
 #include "base/files/file_util.h"
 #include "base/strings/stringize_macros.h"
@@ skipping 31 matching lines @@
 
 void NinjaToolchainWriter::Run() {
   WriteRules();
   WriteSubninjas();
 }
 
 // static
 bool NinjaToolchainWriter::RunAndWriteFile(
     const Settings* settings,
     const Toolchain* toolchain,
-    const std::vector<const Target*>& targets) {
+    std::vector<const Target*>& targets) {
   base::FilePath ninja_file(settings->build_settings()->GetFullPath(
       GetNinjaFileForToolchain(settings)));
   ScopedTrace trace(TraceItem::TRACE_FILE_WRITE, FilePathToUTF8(ninja_file));
 
   base::CreateDirectory(ninja_file.DirName());
 
   std::ofstream file;
   file.open(FilePathToUTF8(ninja_file).c_str(),
             std::ios_base::out | std::ios_base::binary);
   if (file.fail())
     return false;
 
+  // Sort here to ensure the files are deterministically ordered.

[M-A Ruel, 2015/12/07 00:20:16]

You could DCHECK instead that the list is sorted. I'd prefer that to mutating
the inputs.

[Zachary Forman, 2015/12/07 03:18:17]

This is poor phrasing on my part - they come in unsorted and leave sorted.
Making a copy is probably cheap enough, though.

+  std::sort(targets.begin(), targets.end(), DereferenceComparator<Target>());
+
   NinjaToolchainWriter gen(settings, toolchain, targets, file);
   gen.Run();
   return true;
 }
 
 void NinjaToolchainWriter::WriteRules() {
   std::string rule_prefix = GetNinjaRulePrefixForToolchain(settings_);
 
   for (int i = Toolchain::TYPE_NONE + 1; i < Toolchain::TYPE_NUMTYPES; i++) {
     Toolchain::ToolType tool_type = static_cast<Toolchain::ToolType>(i);
@@ skipping 58 matching lines @@
   // Write subninja commands for each generated target.
   for (const auto& target : targets_) {
     OutputFile ninja_file(target->settings()->build_settings(),
                           GetNinjaFileForTarget(target));
     out_ << "subninja ";
     path_output_.WriteFile(out_, ninja_file);
     out_ << std::endl;
   }
   out_ << std::endl;
 }