Add presubmit check for #pragma once.

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 336 matching lines @@
   result = []
   if (warnings):
     result.append(output_api.PresubmitPromptWarning(
         'Banned functions were used.\n' + '\n'.join(warnings)))
   if (errors):
     result.append(output_api.PresubmitError(
         'Banned functions were used.\n' + '\n'.join(errors)))
   return result
 
 
+def _CheckNoPragmaOnce(input_api, output_api):
+  """Make sure that banned functions are not used."""
+  files = []
+  pattern = input_api.re.compile(r'^#pragma\s+once',
+                                 input_api.re.MULTILINE)
+  for f in input_api.AffectedSourceFiles(input_api.FilterSourceFile):
+    if not f.LocalPath().endswith('.h'):
+      continue
+    contents = input_api.ReadFile(f)
+    if pattern.search(contents):
+      files.append(f)
+
+  if files:
+    return [output_api.PresubmitError(
+        'Do not use #pragma once in header files.\n' +

[awong, 2012/07/11 05:41:06]

I don't think you need this plus to concat these strings.  In fact, I think if
you do, you end up making an o(n) copy...

[dcheng, 2012/07/11 05:44:19]

Oops, you're right. I copied this from the iostream check so I'll fix that site
as well.

+        'See http://www.chromium.org/developers/coding-style#TOC-File-headers',
+        files)]
+  return []
+
 
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
   results.extend(input_api.canned_checks.PanProjectChecks(
       input_api, output_api, excluded_paths=_EXCLUDED_PATHS))
   results.extend(_CheckAuthorizedAuthor(input_api, output_api))
   results.extend(
     _CheckNoProductionCodeUsingTestOnlyFunctions(input_api, output_api))
   results.extend(_CheckNoIOStreamInHeaders(input_api, output_api))
   results.extend(_CheckNoUNIT_TESTInSourceFiles(input_api, output_api))
   results.extend(_CheckNoNewWStrings(input_api, output_api))
   results.extend(_CheckNoDEPSGIT(input_api, output_api))
   results.extend(_CheckNoBannedFunctions(input_api, output_api))
+  results.extend(_CheckNoPragmaOnce(input_api, output_api))
   return results
 
 
 def _CheckSubversionConfig(input_api, output_api):
   """Verifies the subversion config file is correctly setup.
 
   Checks that autoprops are enabled, returns an error otherwise.
   """
   join = input_api.os_path.join
   if input_api.platform == 'win32':
@@ skipping 111 matching lines @@
 
   trybots = ['win_rel', 'linux_rel', 'mac_rel', 'linux_clang:compile']
   # match things like aurax11.cc or aura_oak.cc
   if any(re.search('[/_]aura', f) for f in files):
     trybots.append('linux_chromeos')
 
   if not all(f.startswith('chrome/') for f in files):
     trybots.append('android')
 
   return trybots