GN: Makes GN output deterministic

tools/gn/ninja_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_writer.h"
 
 #include "tools/gn/builder.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/location.h"
 #include "tools/gn/ninja_build_writer.h"
 #include "tools/gn/ninja_toolchain_writer.h"
 #include "tools/gn/settings.h"
+#include "tools/gn/target.h"
 
 NinjaWriter::NinjaWriter(const BuildSettings* build_settings,
                          Builder* builder)
     : build_settings_(build_settings),
       builder_(builder) {
 }
 
 NinjaWriter::~NinjaWriter() {
 }
 
 // static
 bool NinjaWriter::RunAndWriteFiles(const BuildSettings* build_settings,
                                    Builder* builder,
                                    Err* err) {
   NinjaWriter writer(build_settings, builder);
 
   std::vector<const Settings*> all_settings;
   std::vector<const Target*> default_targets;
   if (!writer.WriteToolchains(&all_settings, &default_targets, err))

[mithro-old, 2015/12/03 05:20:31]

Doesn't sorting in NinjaWriter::WriteToolchains mean you don't need to sort
here?

[Zachary Forman, 2015/12/03 07:27:02]

Other way around - more than just WriteToolchains calls this function. Good
catch, though.

     return false;
+
+  // Sort the targets so that outputs have a consistent order.

[mithro-old, 2015/12/03 05:20:31]

Can we get a test for this?

[Zachary Forman, 2015/12/03 07:27:02]

I don't think so. It percolates through a stack of other methods, each of which
instantiates more NinjaBuildWriters.

It is probably possible, but I don't know how.

+  std::sort(default_targets.begin(), default_targets.end(),
+            [](const Target* a, const Target* b) { return *a < *b; });

[mithro-old, 2015/12/03 05:20:31]

Can you use your comparator here instead of a lambda?

[Zachary Forman, 2015/12/03 07:27:02]

Yeah, might as well. It'll be a little nicer.

+
   return writer.WriteRootBuildfiles(all_settings, default_targets, err);
 }
 
 // static
 bool NinjaWriter::RunAndWriteToolchainFiles(
     const BuildSettings* build_settings,
     Builder* builder,
     std::vector<const Settings*>* all_settings,
     Err* err) {
   NinjaWriter writer(build_settings, builder);
@@ skipping 20 matching lines @@
     Err(Location(), "No targets.",
         "I could not find any targets to write, so I'm doing nothing.")
         .PrintToStdout();
     return false;
   }
 
   Label default_label = builder_->loader()->GetDefaultToolchain();
 
   // Write out the toolchain buildfiles, and also accumulate the set of
   // all settings and find the list of targets in the default toolchain.
-  for (CategorizedMap::const_iterator i = categorized.begin();
-       i != categorized.end(); ++i) {
+  for (CategorizedMap::iterator i = categorized.begin(); i != categorized.end();
+       ++i) {
     const Settings* settings =
         builder_->loader()->GetToolchainSettings(i->first);
     const Toolchain* toolchain = builder_->GetToolchain(i->first);
 
     all_settings->push_back(settings);
+    // Sort the toolchain's targets to ensure output is consistently ordered.
+    std::sort(i->second.begin(), i->second.end(),

[mithro-old, 2015/12/03 05:20:31]

Same as above...

[Zachary Forman, 2015/12/03 07:27:02]

Acknowledged

+              [](const Target* a, const Target* b) { return *a < *b; });
     if (!NinjaToolchainWriter::RunAndWriteFile(settings, toolchain,
                                                i->second)) {
       Err(Location(),
           "Couldn't open toolchain buildfile(s) for writing").PrintToStdout();
       return false;
     }
   }
 
   *default_targets = categorized[default_label];
   return true;
 }
 
 bool NinjaWriter::WriteRootBuildfiles(
     const std::vector<const Settings*>& all_settings,
     const std::vector<const Target*>& default_targets,
     Err* err) {
   // All Settings objects should have the same default toolchain, and there
   // should always be at least one settings object in the build.
   CHECK(!all_settings.empty());
   const Toolchain* default_toolchain =
       builder_->GetToolchain(all_settings[0]->default_toolchain_label());
 
   // Write the root buildfile.
   return NinjaBuildWriter::RunAndWriteFile(build_settings_, all_settings,
                                            default_toolchain, default_targets,
                                            err);
 }