GN flag to fail for unused build args.

tools/gn/setup.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 "tools/gn/setup.h"
 
 #include <stdlib.h>
 #include <algorithm>
 #include <sstream>
 #include <utility>
@@ skipping 314 matching lines @@
 
 bool Setup::RunPostMessageLoop() {
   Err err;
   if (build_settings_.check_for_bad_items()) {
     if (!builder_->CheckForBadItems(&err)) {
       err.PrintToStdout();
       return false;
     }
 
     if (!build_settings_.build_args().VerifyAllOverridesUsed(&err)) {
-      // TODO(brettw) implement a system of warnings. Until we have a better
-      // system, print the error but don't return failure.
+      // TODO(brettw) implement a system to have a different marker for
+      // warnings. Until we have a better system, print the error but don't
+      // return failure unless requested on the command line.
       err.PrintToStdout();
+      if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+              switches::kFailOnUnusedArgs))
+        return false;
       return true;

[Dirk Pranke, 2016/04/23 01:27:17]

I actually feel (reasonably strongly) that we should fail on unused args by
default, and have the switch *disable* that behavior, at least until we get a
lot more feedback that this is unworkable.

Or, at least, I would say that should be the default and then configurable per
repo via the dotfile.

But, I don't feel so strongly about this that I won't approve this CL.

     }
   }
 
   if (check_public_headers_) {
     std::vector<const Target*> all_targets = builder_->GetAllResolvedTargets();
     std::vector<const Target*> to_check;
     if (check_patterns()) {
       commands::FilterTargetsByPatterns(all_targets, *check_patterns(),
                                         &to_check);
     } else {
@@ skipping 373 matching lines @@
       if (err.has_error()) {
         err.PrintToStdout();
         return false;
       }
     }
     build_settings_.set_exec_script_whitelist(std::move(whitelist));
   }
 
   return true;
 }