Add a GN assert that output dir doesn't have a platform name

build/config/BUILD.gn

 # 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.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/toolchain/goma.gni")
 
 declare_args() {
   # When set (the default) enables C++ iterator debugging in debug builds.
   # Iterator debugging is always off in release builds (technically, this flag
   # affects the "debug" config, which is always available but applied by
   # default only in debug builds).
   #
   # Iterator debugging is generally useful for catching bugs. But it can
   # introduce extra locking to check the state of an iterator against the state
   # of the current object. For iterator- and thread-heavy code, this can
   # significantly slow execution.
   enable_iterator_debugging = true
 
   # Set to true to enable dcheck in Release builds.
   dcheck_always_on = false
 }
 
+# Because of the source assignment filter, many targets end up over-filtering
+# their sources if the output directory contains a platform name. Assert that
+# this doesn't happen. http://crbug.com/548283
+template("assert_valid_out_dir") {
+  assert(target_name != "")  # Mark as used.
+  assert(
+      invoker.sources == invoker.actual_sources,
+      "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
+}
+
+assert_valid_out_dir("_check_output_dir_has_no_platform_name") {
+  actual_sources = [ "$root_build_dir/foo" ]
+  sources = actual_sources
+}
+
 # TODO(brettw) Most of these should be removed. Instead of global feature
 # flags, we should have more modular flags that apply only to a target and its
 # dependents. For example, depending on the "x11" meta-target should define
 # USE_X11 for all dependents so that everything that could use X11 gets the
 # define, but anything that doesn't depend on X11 doesn't see it.
 #
 # For now we define these globally to match the current GYP build.
 config("feature_flags") {
   # TODO(brettw) this probably needs to be parameterized.
   defines = [
@@ skipping 421 matching lines @@
     # This error doesn't happen every time. In VS2013, it seems if the .pch
     # file doesn't exist, no error will be generated (probably MS tested this
     # case but forgot the other one?). To reproduce this error, do a build,
     # then delete the precompile.c.obj file, then build again.
     cflags_c = [ "/wd4206" ]
   } else if (is_mac && !is_official_build && !use_goma) {
     precompiled_header = "build/precompile.h"
     precompiled_source = "//build/precompile.h"
   }
 }