Add a canned clang-format presubmit check

git_cl.py

 #!/usr/bin/env python
 # 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 62 matching lines @@
           'Command "%s" failed.\n%s' % (
             ' '.join(args), error_message or e.stdout or ''))
     return e.stdout
 
 
 def RunGit(args, **kwargs):
   """Returns stdout."""
   return RunCommand(['git'] + args, **kwargs)
 
 
-def RunGitWithCode(args):
+def RunGitWithCode(args, suppress_stderr=False):
   """Returns return code and stdout."""
   try:
     env = os.environ.copy()
     # 'cat' is a magical git string that disables pagers on all platforms.
     env['GIT_PAGER'] = 'cat'
+    if suppress_stderr:
+      stderr = subprocess2.VOID
+    else:
+      stderr = sys.stderr
     out, code = subprocess2.communicate(['git'] + args,
                                         env=env,
-                                        stdout=subprocess2.PIPE)
+                                        stdout=subprocess2.PIPE,
+                                        stderr=stderr)
     return code, out[0]
   except ValueError:
     # When the subprocess fails, it returns None.  That triggers a ValueError
     # when trying to unpack the return value into (out, code).
     return 1, ''
 
 
 def IsGitVersionAtLeast(min_version):
   prefix = 'git version '
   version = RunGit(['--version']).strip()
@@ skipping 2192 matching lines @@
       [f.LocalPath() for f in
           cl.GetChange(base_branch, None).AffectedFiles()],
       change.RepositoryRoot(), author,
       fopen=file, os_path=os.path, glob=glob.glob,
       disable_color=options.no_color).run()
 
 
 def CMDformat(parser, args):
   """Runs clang-format on the diff."""
   CLANG_EXTS = ['.cc', '.cpp', '.h']
-  parser.add_option('--full', action='store_true', default=False)
+  parser.add_option('--full', action='store_true',
+                    help='Reformat the full content of all touched files')
+  parser.add_option('--dry-run', action='store_true',
+                    help='Don\'t modify any file on disk.')
   opts, args = parser.parse_args(args)
   if args:
     parser.error('Unrecognized args: %s' % ' '.join(args))
 
   # git diff generates paths against the root of the repository.  Change
   # to that directory so clang-format can find files even within subdirs.
   rel_base_path = RunGit(['rev-parse', '--show-cdup']).strip()
   if rel_base_path:
     os.chdir(rel_base_path)
 
@@ skipping 36 matching lines @@
     clang_format_tool = clang_format.FindClangFormatToolInChromiumTree()
   except clang_format.NotFoundError, e:
     DieWithError(e)
 
   if opts.full:
     # diff_output is a list of files to send to clang-format.
     files = diff_output.splitlines()
     if not files:
       print "Nothing to format."
       return 0
-    RunCommand([clang_format_tool, '-i'] + files,
-               cwd=top_dir)
+    cmd = [clang_format_tool]
+    if not opts.dry_run:
+      cmd.append('-i')
+    stdout = RunCommand(cmd + files, cwd=top_dir)
   else:
     env = os.environ.copy()
     env['PATH'] = os.path.dirname(clang_format_tool)
     # diff_output is a patch to send to clang-format-diff.py
     try:
       script = clang_format.FindClangFormatScriptInChromiumTree(
           'clang-format-diff.py')
     except clang_format.NotFoundError, e:
       DieWithError(e)
 
-    cmd = [sys.executable, script, '-p0', '-i']
+    cmd = [sys.executable, script, '-p0']
+    if not opts.dry_run:
+      cmd.append('-i')
 
-    RunCommand(cmd, stdin=diff_output, cwd=top_dir, env=env)
+    stdout = RunCommand(cmd, stdin=diff_output, cwd=top_dir, env=env)
+    if opts.dry_run and len(stdout) > 0:
+      return 2
 
   return 0
 
 
 class OptionParser(optparse.OptionParser):
   """Creates the option parse and add --verbose support."""
   def __init__(self, *args, **kwargs):
     optparse.OptionParser.__init__(
         self, *args, prog='git cl', version=__version__, **kwargs)
     self.add_option(
@@ skipping 29 matching lines @@
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   sys.exit(main(sys.argv[1:]))