Add toolchains to dependency error messages in GN

tools/gn/command_gen.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 "base/atomicops.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/timer/elapsed_timer.h"
@@ skipping 53 matching lines @@
   return nullptr;
 }
 
 // Prints an error that the given file was present as a source or input in
 // the given target(s) but was not generated by any of its dependencies.
 void PrintInvalidGeneratedInput(const Builder* builder,
                                 const SourceFile& file,
                                 const std::vector<const Target*>& targets) {
   std::string err;
 
+  // Only show the toolchain labels (which can be confusing) if something
+  // isn't the default.
+  bool show_toolchains = false;
+  const Label& default_toolchain =
+      targets[0]->settings()->default_toolchain_label();
+  for (const Target* target : targets) {
+    if (target->settings()->toolchain_label() != default_toolchain) {
+      show_toolchains = true;
+      break;
+    }
+  }
+
+  const Target* generator = FindTargetThatGeneratesFile(builder, file);
+  if (generator &&
+      generator->settings()->toolchain_label() != default_toolchain)
+    show_toolchains = true;
+
   const std::string target_str = targets.size() > 1 ? "targets" : "target";
   err += "The file:\n";
   err += "  " + file.value() + "\n";
   err += "is listed as an input or source for the " + target_str + ":\n";
   for (const Target* target : targets)
-    err += "  " + target->label().GetUserVisibleName(false) + "\n";
+    err += "  " + target->label().GetUserVisibleName(show_toolchains) + "\n";
 
-  const Target* generator = FindTargetThatGeneratesFile(builder, file);
   if (generator) {
     err += "but this file was not generated by any dependencies of the " +
         target_str + ". The target\nthat generates the file is:\n  ";
-    err += generator->label().GetUserVisibleName(false);
+    err += generator->label().GetUserVisibleName(show_toolchains);
   } else {
     err += "but no targets in the build generate that file.";
   }
 
   Err(Location(), "Input to " + target_str + " not generated by a dependency.",
       err).PrintToStdout();
 }
 
 bool CheckForInvalidGeneratedInputs(Setup* setup) {
   std::multimap<SourceFile, const Target*> unknown_inputs =
@@ skipping 110 matching lines @@
             setup->scheduler().input_file_manager()->GetInputFileCount()) +
         " files in " +
         base::Int64ToString(elapsed_time.InMilliseconds()) + "ms\n";
     OutputString(stats);
   }
 
   return 0;
 }
 
 }  // namespace commands