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..f2c6d98532756d25c97414e5f0704b625df77109 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 +31,11 @@ bool NinjaWriter::RunAndWriteFiles(const BuildSettings* build_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);
 }
 
@@ -70,13 +76,16 @@ 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();
+       ++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(),