Add PRESUBMIT check for #ifdefs on values that are always defined.

PRESUBMIT.py

 # 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 1265 matching lines @@
   results.extend(_CheckNoTrinaryTrueFalse(input_api, output_api))
   results.extend(_CheckUnwantedDependencies(input_api, output_api))
   results.extend(_CheckFilePermissions(input_api, output_api))
   results.extend(_CheckNoAuraWindowPropertyHInHeaders(input_api, output_api))
   results.extend(_CheckIncludeOrder(input_api, output_api))
   results.extend(_CheckForVersionControlConflicts(input_api, output_api))
   results.extend(_CheckPatchFiles(input_api, output_api))
   results.extend(_CheckHardcodedGoogleHostsInLowerLayers(input_api, output_api))
   results.extend(_CheckNoAbbreviationInPngFileName(input_api, output_api))
   results.extend(_CheckForInvalidOSMacros(input_api, output_api))
+  results.extend(_CheckForInvalidIfDefinedMacros(input_api, output_api))
   results.extend(_CheckAddedDepsHaveTargetApprovals(input_api, output_api))
   results.extend(
       input_api.canned_checks.CheckChangeHasNoTabs(
           input_api,
           output_api,
           source_file_filter=lambda x: x.LocalPath().endswith('.grd')))
   results.extend(_CheckSpamLogging(input_api, output_api))
   results.extend(_CheckForAnonymousVariables(input_api, output_api))
   results.extend(_CheckCygwinShell(input_api, output_api))
   results.extend(_CheckUserActionUpdate(input_api, output_api))
@@ skipping 90 matching lines @@
     if not f.LocalPath().endswith(('.py', '.js', '.html', '.css')):
       bad_macros.extend(_CheckForInvalidOSMacrosInFile(input_api, f))
 
   if not bad_macros:
     return []
 
   return [output_api.PresubmitError(
       'Possibly invalid OS macro[s] found. Please fix your code\n'
       'or add your macro to src/PRESUBMIT.py.', bad_macros)]
 
+
+def _CheckForInvalidIfDefinedMacrosInFile(input_api, f):
+  """Check all affected files for invalid "if defined" macros."""
+  ALWAYS_DEFINED_MACROS = (
+      "TARGET_CPU_PPC",
+      "TARGET_CPU_PPC64",
+      "TARGET_CPU_68K",
+      "TARGET_CPU_X86",
+      "TARGET_CPU_ARM",
+      "TARGET_CPU_MIPS",
+      "TARGET_CPU_SPARC",
+      "TARGET_CPU_ALPHA",
+      "TARGET_IPHONE_SIMULATOR",
+      "TARGET_OS_EMBEDDED",
+      "TARGET_OS_IPHONE",
+      "TARGET_OS_MAC",
+      "TARGET_OS_UNIX",
+      "TARGET_OS_WIN32",
+  )
+  ifdef_macro = input_api.re.compile(r'^\s*#.*(?:ifdef\s|defined\()([^\s\)]+)')
+  results = []
+  for lnum, line in f.ChangedContents():
+    for match in ifdef_macro.finditer(line):
+      if match.group(1) in ALWAYS_DEFINED_MACROS:
+        always_defined = ' %s is always defined. ' % match.group(1)
+        did_you_mean = 'Did you mean \'#if %s\'?' % match.group(1)
+        results.append('    %s:%d %s\n\t%s' % (f.LocalPath(),
+                                               lnum,
+                                               always_defined,
+                                               did_you_mean))
+  return results
+
+
+def _CheckForInvalidIfDefinedMacros(input_api, output_api):
+  """Check all affected files for invalid "if defined" macros."""
+  bad_macros = []
+  for f in input_api.AffectedFiles():
+    if f.LocalPath().endswith(('.h', '.c', '.cc', '.m', '.mm')):
+      bad_macros.extend(_CheckForInvalidIfDefinedMacrosInFile(input_api, f))
+
+  if not bad_macros:
+    return []
+
+  return [output_api.PresubmitError(
+      'Found ifdef check on always-defined macro[s]. Please fix your code\n'
+      'or check the list of ALWAYS_DEFINED_MACROS in src/PRESUBMIT.py.',
+      bad_macros)]
+
+
 def _CheckForIPCRules(input_api, output_api):
   """Check for same IPC rules described in
   http://www.chromium.org/Home/chromium-security/education/security-tips-for-ipc
   """
   base_pattern = r'IPC_ENUM_TRAITS\('
   inclusion_pattern = input_api.re.compile(r'(%s)' % base_pattern)
   comment_pattern = input_api.re.compile(r'//.*(%s)' % base_pattern)
 
   problems = []
   for f in input_api.AffectedSourceFiles(None):
@@ skipping 241 matching lines @@
     builders.extend(['cros_x86'])
 
   # The AOSP bot doesn't build the chrome/ layer, so ignore any changes to it
   # unless they're .gyp(i) files as changes to those files can break the gyp
   # step on that bot.
   if (not all(re.search('^chrome', f) for f in files) or
       any(re.search('\.gypi?$', f) for f in files)):
     builders.extend(['android_aosp'])
 
   return GetDefaultTryConfigs(builders)