GN: Makes GN output deterministic

tools/gn/ninja_build_writer.cc

Index: tools/gn/ninja_build_writer.cc
diff --git a/tools/gn/ninja_build_writer.cc b/tools/gn/ninja_build_writer.cc
index 50638fbb7876819438dea2b6dbe659779da72731..67c2c87781814adf176e3bbe77d06a8903c6456c 100644
--- a/tools/gn/ninja_build_writer.cc
+++ b/tools/gn/ninja_build_writer.cc
@@ -194,13 +194,18 @@ void NinjaBuildWriter::WriteNinjaRules() {
   dep_out_ << "build.ninja:";
   std::vector<base::FilePath> input_files;
   g_scheduler->input_file_manager()->GetAllPhysicalInputFileNames(&input_files);
-  for (const auto& input_file : input_files)
-    dep_out_ << " " << FilePathToUTF8(input_file);
+
+  // Put the files into a set so that the output is sorted and hence

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

Why not just std::sort(input_files.begin(), input_files.end());

That would be faster than creating a second structure in memory.

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

Interestingly, the two vectors seem to contain a non-deterministic number of
targets, and either one might contain duplicates.
The purpose of the std::set here is both to sort the output and remove
duplicates.

This could be better commented, so I'll clarify that in the comment :).

+  // deterministic.
+  std::set<base::FilePath> file_set(input_files.begin(), input_files.end());
 
   // Other files read by the build.
-  std::vector<base::FilePath> other_files = g_scheduler->GetGenDependencies();
-  for (const auto& other_file : other_files)
-    dep_out_ << " " << FilePathToUTF8(other_file);
+  input_files = g_scheduler->GetGenDependencies();
+
+  file_set.insert(input_files.begin(), input_files.end());
+
+  for (const auto& input_file : file_set)
+    dep_out_ << " " << FilePathToUTF8(input_file);
 
   out_ << std::endl;
 }