experiment with -Wimplicit-fallthrough

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 2463 matching lines @@
         ],
       }],
       ['chromium_code==0', {
         'conditions': [
           [ 'os_posix==1 and OS!="mac" and OS!="ios"', {
             # We don't want to get warnings from third-party code,
             # so remove any existing warning-enabling flags like -Wall.
             'cflags!': [
               '-Wall',
               '-Wextra',
+              '-Wimplicit-fallthrough',
             ],
             'cflags_cc': [
               # Don't warn about hash_map in third-party code.
               '-Wno-deprecated',
             ],
             'cflags': [
               # Don't warn about printf format problems.
               # This is off by default in gcc but on in Ubuntu's gcc(!).
               '-Wno-format',
             ],
@@ skipping 41 matching lines @@
             ],
           }],
           # TODO(darin): Unfortunately, some third_party code depends on base.
           [ 'OS=="win" and component=="shared_library"', {
             'msvs_disabled_warnings': [
               4251,  # class 'std::xx' needs to have dll-interface.
             ],
           }],
           [ 'OS=="mac" or OS=="ios"', {
             'xcode_settings': {
-              'WARNING_CFLAGS!': ['-Wall', '-Wextra'],
+              'WARNING_CFLAGS!': ['-Wall', '-Wextra', '-Wimplicit-fallthrough'],
             },
             'conditions': [
               ['buildtype=="Official"', {
                 'xcode_settings': {
                   'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO',    # -Werror
                 },
               }],
             ],
           }],
           [ 'OS=="ios"', {
@@ skipping 743 matching lines @@
                 ],
                 'ldflags': [
                   '--sysroot=<(sysroot)',
                   '<!(<(DEPTH)/build/linux/sysroot_ld_path.sh <(sysroot))',
                 ],
               }]]
           }],
           ['clang==1', {
             'cflags': [
               '-Wheader-hygiene',
+              '-Wimplicit-fallthrough',
 
               # Don't die on dtoa code that uses a char as an array index.
               '-Wno-char-subscripts',
 
               # TODO(thakis): This used to be implied by -Wno-unused-function,
               # which we no longer use. Check if it makes sense to remove
               # this as well. http://crbug.com/316352
               '-Wno-unneeded-internal-declaration',
 
               # Warns on switches on enums that cover all enum values but
@@ skipping 684 matching lines @@
               # TODO(thakis): Eventually switch this to c++11 instead of
               # gnu++11 (once typeof can be removed, which is blocked on c++11
               # being available everywhere).
               'CLANG_CXX_LANGUAGE_STANDARD': 'gnu++11',  # -std=gnu++11
               # Warn if automatic synthesis is triggered with
               # the -Wobjc-missing-property-synthesis flag.
               'CLANG_WARN_OBJC_MISSING_PROPERTY_SYNTHESIS': 'YES',
               'GCC_VERSION': 'com.apple.compilers.llvm.clang.1_0',
               'WARNING_CFLAGS': [
                 '-Wheader-hygiene',
+                '-Wimplicit-fallthrough',
 
                 # This warns on using ints as initializers for floats in
                 # initializer lists (e.g. |int a = f(); CGSize s = { a, a };|),
                 # which happens in several places in chrome code. Not sure if
                 # this is worth fixing.
                 '-Wno-c++11-narrowing',
 
                 # Don't die on dtoa code that uses a char as an array index.
                 # This is required solely for base/third_party/dmg_fp/dtoa.cc.
                 '-Wno-char-subscripts',
@@ skipping 758 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }