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.
+  set_sources_assignment_filter([

[brettw, 2016/02/16 19:19:58]

This is a clever idea!

I *think* the default sources assignment filter will apply without you doing
this. Does this test work if you just delete the set_... call? I would expect
that test will validate the current filter on the current platform without the
possibility of any skew in what the filter is and what you list out here.

[agrieve, 2016/02/16 20:04:20]

I had thought the same, but then figured it wouldn't catch the case of the
current platform being used. Just tried it however, and it worked just fine
(triggered the assert for is_android & "android").

Maybe this is the case due to a dep on a target($host_toolchain), which would
then have a linux filter?

Either way, it works, so i've made the change. :)

+                                  "*\bandroid/*",
+                                  "*\bchromeos/*",
+                                  "*\bcocoa/*",
+                                  "*\bios/*",
+                                  "*\blinux/*",
+                                  "*\bmac/*",
+                                  "*\bposix/*",
+                                  "*\bwin/*",
+                                ])
+
+  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"
   }
 }