GN: Generate error if multiple rules generate same file

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 1436af6da7e2ff0ce77e18f967b9b177c3d98f64..519b09c6aec84164c45b76fa56690dc3821aeaa4 100644
--- a/tools/gn/ninja_build_writer.cc
+++ b/tools/gn/ninja_build_writer.cc
@@ -15,6 +15,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "tools/gn/build_settings.h"
+#include "tools/gn/err.h"
 #include "tools/gn/escape.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/input_file_manager.h"
@@ -91,11 +92,11 @@ NinjaBuildWriter::NinjaBuildWriter(
 NinjaBuildWriter::~NinjaBuildWriter() {
 }
 
-void NinjaBuildWriter::Run() {
+bool NinjaBuildWriter::Run() {

[brettw, 2014/09/26 18:01:20]

Yeah, this should probably take an Err* out param.

   WriteNinjaRules();
   WriteLinkPool();
   WriteSubninjas();
-  WritePhonyAndAllRules();
+  return WritePhonyAndAllRules();
 }
 
 // static
@@ -124,8 +125,7 @@ bool NinjaBuildWriter::RunAndWriteFile(
 
   NinjaBuildWriter gen(build_settings, all_settings, default_toolchain,
                        default_toolchain_targets, file, depfile);
-  gen.Run();
-  return true;
+  return gen.Run();
 }
 
 void NinjaBuildWriter::WriteNinjaRules() {
@@ -171,7 +171,7 @@ void NinjaBuildWriter::WriteSubninjas() {
   out_ << std::endl;
 }
 
-void NinjaBuildWriter::WritePhonyAndAllRules() {
+bool NinjaBuildWriter::WritePhonyAndAllRules() {
   std::string all_rules;
 
   // Write phony rules for all uniquely-named targets in the default toolchain.
@@ -180,6 +180,7 @@ void NinjaBuildWriter::WritePhonyAndAllRules() {
   // which we also find.
   std::map<std::string, int> small_name_count;
   std::vector<const Target*> toplevel_targets;
+  base::hash_set<std::string> target_files;
   for (size_t i = 0; i < default_toolchain_targets_.size(); i++) {
     const Target* target = default_toolchain_targets_[i];
     const Label& label = target->label();
@@ -204,6 +205,11 @@ void NinjaBuildWriter::WritePhonyAndAllRules() {
     OutputFile target_file(target->dependency_output_file());
     // The output files may have leading "./" so normalize those away.
     NormalizePath(&target_file.value());
+    if (!target_files.insert(target_file.value()).second) {
+      Err(Location(), "Duplicate rules for " + target_file.value())
+          .PrintToStdout();
+      return false;
+    }
 
     // Write the long name "foo/bar:baz" for the target "//foo/bar:baz".
     std::string long_name = label.GetUserVisibleName(false);
@@ -244,6 +250,7 @@ void NinjaBuildWriter::WritePhonyAndAllRules() {
     out_ << "\nbuild all: phony " << all_rules << std::endl;
     out_ << "default all" << std::endl;
   }
+  return true;
 }
 
 void NinjaBuildWriter::WritePhonyRule(const Target* target,