Add git cl format --diff option to print format diff without modifying files

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 2317 matching lines @@
 
 
 @subcommand.usage('[files or directories to diff]')
 def CMDformat(parser, args):
   """Runs clang-format on the diff."""
   CLANG_EXTS = ['.cc', '.cpp', '.h', '.mm', '.proto']
   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.')
+  parser.add_option('--diff', action='store_true',
+                    help='Print diff to stdout rather than modifying files.')
   opts, args = parser.parse_args(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 = settings.GetRelativeRoot()
   if rel_base_path:
     os.chdir(rel_base_path)
 
   # Generate diff for the current branch's changes.
   diff_cmd = ['diff', '--no-ext-diff', '--no-prefix']
@@ skipping 44 matching lines @@
   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
     cmd = [clang_format_tool]
-    if not opts.dry_run:
+    if not opts.dry_run and not opts.diff:
       cmd.append('-i')
     stdout = RunCommand(cmd + files, cwd=top_dir)
+    if opts.diff:
+      sys.stdout.write(stdout)
   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']
-    if not opts.dry_run:
+    if not opts.dry_run and not opts.diff:
       cmd.append('-i')
 
     stdout = RunCommand(cmd, stdin=diff_output, cwd=top_dir, env=env)
+    if opts.diff:
+      sys.stdout.write(stdout)
     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__(
@@ skipping 31 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:]))