Add support for turning on -Wextra on the mac. Doesn't compile that way, but...

build/common.gypi

 # Copyright (c) 2010 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': {
     # .gyp files or targets should set chromium_code to 1 if they build
@@ skipping 148 matching lines @@
     # MAC_OS_X_VERSION_MIN_REQUIRED compile-time macro.
     # To ensure these macros are available, #include <AvailabilityMacros.h>.
     # Additional documentation on these macros is available at
     # http://developer.apple.com/mac/library/technotes/tn2002/tn2064.html#SECTION3
     # Chrome normally builds with the Mac OS X 10.5 SDK and sets the
     # deployment target to 10.5.  Other projects, such as O3D, may override
     # these defaults.
     'mac_sdk%': '10.5',
     'mac_deployment_target%': '10.5',
 
+    # Turn on -Wextra on chromium code during Mac compile.
+    # TODO(mark,tvl): drop this and turn it always on when it works.
+    'chromium_mac_wextra%': 0,
+
     # Set to 1 to enable code coverage.  In addition to build changes
     # (e.g. extra CFLAGS), also creates a new target in the src/chrome
     # project file called "coverage".
     # Currently ignored on Windows.
     'coverage%': 0,
 
     # Overridable specification for potential use of alternative
     # JavaScript engines.
     'javascript_engine%': 'v8',
 
@@ skipping 335 matching lines @@
             'msvs_settings': {
               'VCCLCompilerTool': {
                 'WarnAsError': 'false',
                 'Detect64BitPortabilityProblems': 'false',
               },
             },
           }],
           [ 'OS=="mac"', {
             'xcode_settings': {
               'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO',
-              'WARNING_CFLAGS!': ['-Wall'],
+              'WARNING_CFLAGS!': ['-Wall', "-Wextra"],

[Mark Mentovai, 2010/06/14 19:13:33]

The adjacent strings use 'single qutoes' instead of "double quotes."

             },
           }],
         ],
       }, {
         # In Chromium code, we define __STDC_FORMAT_MACROS in order to get the
         # C99 macros on Mac and Linux.
         'defines': [
           '__STDC_FORMAT_MACROS',
         ],
         'conditions': [
@@ skipping 605 matching lines @@
           'GCC_WARN_ABOUT_MISSING_NEWLINE': 'YES',  # -Wnewline-eof
           # MACOSX_DEPLOYMENT_TARGET maps to -mmacosx-version-min
           'MACOSX_DEPLOYMENT_TARGET': '<(mac_deployment_target)',
           'PREBINDING': 'NO',                       # No -Wl,-prebind
           'USE_HEADERMAP': 'NO',
           'WARNING_CFLAGS': ['-Wall', '-Wendif-labels'],
           'conditions': [
             ['chromium_mac_pch', {'GCC_PRECOMPILE_PREFIX_HEADER': 'YES'},
                                  {'GCC_PRECOMPILE_PREFIX_HEADER': 'NO'}
             ],
+            ['chromium_mac_wextra', {
+              'WARNING_CFLAGS': [
+                '-Wextra',
+                # Don't warn about unused function params.  Used everywhere.
+                '-Wno-unused-parameter',
+                # Don't warn about the "struct foo f = {0};" initialization
+                # pattern.
+                '-Wno-missing-field-initializers',
+              ]
+            }],
           ],
         },
         'target_conditions': [
           ['_type!="static_library"', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-search_paths_first']},
           }],
           ['_mac_bundle', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-ObjC']},
           }],
           ['_type=="executable" or _type=="shared_library" or _type=="loadable_module"', {
@@ skipping 219 matching lines @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
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