experiment with -Wimplicit-fallthrough

sdch/sdch.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 40 matching lines @@
         'include_dirs': [
           'open-vcdiff/src',
         ],
       },
       'conditions': [
         [ 'OS == "linux" or OS == "android"', { 'include_dirs': [ 'linux' ] } ],
         [ 'os_bsd==1 or OS=="solaris"', { 'include_dirs': [ 'bsd' ] } ],
         [ 'OS == "ios"', { 'include_dirs': [ 'ios' ] } ],
         [ 'OS == "mac"', { 'include_dirs': [ 'mac' ] } ],
         [ 'OS == "win"', { 'include_dirs': [ 'open-vcdiff/vsprojects' ] } ],
-        # TODO(mark): Remove usage of the deprecated auto_ptr.
-        [ 'clang == 1', { 'cflags': [ '-Wno-deprecated-declarations' ] } ],
+        ['clang==1', {
+          # open-vcdiff uses intentional fallthroughs.
+          'xcode_settings': { 'WARNING_CFLAGS!': [ '-Wimplicit-fallthrough' ] },
+          'cflags!': [ '-Wimplicit-fallthrough' ],
+          # TODO(mark): Remove usage of the deprecated auto_ptr.
+          'cflags': [ '-Wno-deprecated-declarations' ] }
+        }],
       ],
       # open-vcdiff's logging.h introduces static initializers. This was
       # reported upstream years ago (
       # https://code.google.com/p/open-vcdiff/issues/detail?id=33 ). Since
       # upstream won't fix this, work around it on the chromium side:
       # Inject a header that forwards to base/logging.h instead (which doesn't
       # introduce static initializers, and which prevents open-vcdiff's
       # logging.h from being used).
       'variables': {
         'logging_path': 'logging_forward.h',
@@ skipping 12 matching lines @@
       # ForcedIncludeFiles is relative to include_dirs, cflags relative to the
       # build directory.
       'xcode_settings': { 'GCC_PREFIX_HEADER': '<(logging_path)' },
       'msvs_settings': {
         'VCCLCompilerTool': { 'ForcedIncludeFiles': [ 'sdch/<(logging_path)' ] }
       },
       'cflags': [ '-include', '<(logging_dir)/sdch/<(logging_path)' ],
     },
   ],
 }