Add the -Wobjc-missing-property-synthesis flag.

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 3051 matching lines @@
           'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',      # -fvisibility=hidden
           'GCC_THREADSAFE_STATICS': 'NO',           # -fno-threadsafe-statics
           'GCC_TREAT_WARNINGS_AS_ERRORS': 'YES',    # -Werror
           'GCC_VERSION': '4.2',
           'GCC_WARN_ABOUT_MISSING_NEWLINE': 'YES',  # -Wnewline-eof
           'USE_HEADERMAP': 'NO',
           'WARNING_CFLAGS': [
             '-Wall',
             '-Wendif-labels',
             '-Wextra',
+            # Warn if automatic synthesis is triggered.
+            '-Wobjc-missing-property-synthesis',

[Nico, 2012/11/14 21:06:55]

If you say 'CLANG_WARN_OBJC_MISSING_PROPERTY_SYNTHESIS': 'YES' instead, then the
UI will know about this warning too. (ninja won't, but that'd be easy to add.)

If you want to keep the flag, it should probably go in the clang==1 block below

[Mark Mentovai, 2012/11/15 00:06:52]

There’s a symbolic name for this

CLANG_WARN_OBJC_MISSING_PROPERTY_SYNTHESIS

which you can set to YES above (and then put a comment saying
-Wobjc-missing-property-synthesis per the rest of the compiler options). Does
that work?

We would also need to add ninja support for this symbolic name. We generally use
those symbolic names when they’re available.

             # Don't warn about unused function parameters.
             '-Wno-unused-parameter',
             # Don't warn about the "struct foo f = {0};" initialization
             # pattern.
             '-Wno-missing-field-initializers',
           ],
           'conditions': [
             ['chromium_mac_pch', {'GCC_PRECOMPILE_PREFIX_HEADER': 'YES'},
                                  {'GCC_PRECOMPILE_PREFIX_HEADER': 'NO'}
             ],
@@ skipping 226 matching lines @@
     ['OS=="ios"', {
       'target_defaults': {
         'xcode_settings' : {
           'GCC_VERSION': 'com.apple.compilers.llvm.clang.1_0',
 
           # This next block is mostly common with the 'mac' section above,
           # but keying off (or setting) 'clang' isn't valid for iOS as it
           # also seems to mean using the custom build of clang.
 
           # Don't use -Wc++0x-extensions, which Xcode 4 enables by default
-          # when buliding with clang. This warning is triggered when the
+          # when building with clang. This warning is triggered when the
           # override keyword is used via the OVERRIDE macro from
           # base/compiler_specific.h.
           'CLANG_WARN_CXX0X_EXTENSIONS': 'NO',
           'WARNING_CFLAGS': [
             '-Wheader-hygiene',
             # 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',
             # Clang spots more unused functions.
             '-Wno-unused-function',
             # See comments on this flag higher up in this file.
             '-Wno-unnamed-type-template-args',
-            # This (rightyfully) complains about 'override', which we use
+            # This (rightfully) complains about 'override', which we use
             # heavily.
             '-Wno-c++11-extensions',
           ],
         },
         'target_conditions': [
           ['_type=="executable"', {
             'configurations': {
               'Release_Base': {
                 'xcode_settings': {
                   'DEPLOYMENT_POSTPROCESSING': 'YES',
@@ skipping 391 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',
   },
 }