GN: Makes GN output deterministic

tools/gn/ninja_writer.cc

Index: tools/gn/ninja_writer.cc
diff --git a/tools/gn/ninja_writer.cc b/tools/gn/ninja_writer.cc
index 23b9a72f8f913ff08f1b2ca1b10e430711106795..c8c8c9dfc29d6d2538e6625639d816b544d12ead 100644
--- a/tools/gn/ninja_writer.cc
+++ b/tools/gn/ninja_writer.cc
@@ -10,6 +10,7 @@
 #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)
@@ -30,6 +31,12 @@ bool NinjaWriter::RunAndWriteFiles(const BuildSettings* build_settings,
   std::vector<const Target*> default_targets;
   if (!writer.WriteToolchains(&all_settings, &default_targets, err))
     return false;
+
+  // Sort targets so that they are in a deterministic order.

[M-A Ruel, 2015/12/07 15:09:50]

I'd prefer WriteToolchains() to return a sorted list instead.

[Zachary Forman, 2015/12/08 09:40:43]

This is a good idea. It'll improve speed (as the work was currently duplicated).

+  std::sort(
+      default_targets.begin(), default_targets.end(),
+      [](const Target* a, const Target* b) { return a->label() < b->label(); });
+
   return writer.WriteRootBuildfiles(all_settings, default_targets, err);
 }
 
@@ -70,13 +77,14 @@ bool NinjaWriter::WriteToolchains(std::vector<const Settings*>* all_settings,
 
   // 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();

[M-A Ruel, 2015/12/07 15:09:50]

If you use a set above, you can switch to an enumeration using "const auto&"

[Zachary Forman, 2015/12/08 09:40:42]

Have done.

+       ++i) {
     const Settings* settings =
         builder_->loader()->GetToolchainSettings(i->first);
     const Toolchain* toolchain = builder_->GetToolchain(i->first);
 
     all_settings->push_back(settings);
+
     if (!NinjaToolchainWriter::RunAndWriteFile(settings, toolchain,
                                                i->second)) {
       Err(Location(),