Default to using --3way when using `git cl patch` with git >= 1.7.12

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."""
 
 import difflib
+from distutils.version import LooseVersion
 import json
 import logging
 import optparse
 import os
 import re
 import stat
 import sys
 import textwrap
 import urllib2
 import urlparse
@@ skipping 60 matching lines @@
     out, code = subprocess2.communicate(['git'] + args,
                                         env=env,
                                         stdout=subprocess2.PIPE)
     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()
+  return (version.startswith(PREFIX) and
+      LooseVersion(version[len(PREFIX):]) >= LooseVersion(min_version))
+
+
 def usage(more):
   def hook(fn):
     fn.usage_more = more
     return fn
   return hook
 
 
 def ask_for_data(prompt):
   try:
     return raw_input(prompt)
@@ skipping 1606 matching lines @@
 
 
 @usage('<patch url or issue id>')
 def CMDpatch(parser, args):
   """patch in a code review"""
   parser.add_option('-b', dest='newbranch',
                     help='create a new branch off trunk for the patch')
   parser.add_option('-f', action='store_true', dest='force',
                     help='with -b, clobber any existing branch')
   parser.add_option('--reject', action='store_true', dest='reject',
-                    help='allow failed patches and spew .rej files')
+                    help='failed patches spew .rej files rather than '
+                        'attempting a 3-way merge')
   parser.add_option('-n', '--no-commit', action='store_true', dest='nocommit',
                     help="don't commit after patch applies")
   (options, args) = parser.parse_args(args)
   if len(args) != 1:
     parser.print_help()
     return 1
   issue_arg = args[0]
 
   # TODO(maruel): Use apply_issue.py
   # TODO(ukai): use gerrit-cherry-pick for gerrit repository?
@@ skipping 41 matching lines @@
   env = os.environ.copy()
   # 'cat' is a magical git string that disables pagers on all platforms.
   env['GIT_PAGER'] = 'cat'
 
   # We use "git apply" to apply the patch instead of "patch" so that we can
   # pick up file adds.
   # The --index flag means: also insert into the index (so we catch adds).
   cmd = ['git', 'apply', '--index', '-p0']
   if options.reject:
     cmd.append('--reject')
+  elif IsGitVersionAtLeast('1.7.12'):
+    cmd.append('--3way')
   try:
     subprocess2.check_call(cmd, env=env,
                            stdin=patch_data, stdout=subprocess2.VOID)
   except subprocess2.CalledProcessError:
     DieWithError('Failed to apply the patch')
 
   # If we had an issue, commit the current state and register the issue.
   if not options.nocommit:
     RunGit(['commit', '-m', 'patch from issue %s' % issue])
     cl = Changelist()
@@ skipping 377 matching lines @@
   GenUsage(parser, 'help')
   return CMDhelp(parser, argv)
 
 
 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:]))