Make git.checkout return the commit hash.

recipe_modules/git/api.py

 # Copyright 2013 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.
 
 import itertools
 import re
 
 from recipe_engine import recipe_api
 
 class GitApi(recipe_api.RecipeApi):
@@ skipping 122 matching lines @@
           a side effect of all stderr output of 'git fetch' going to that file.
       can_fail_build (bool): if False, ignore errors during fetch or checkout.
       set_got_revision (bool): if True, resolves HEAD and sets got_revision
           property.
       remote_name (str): name of the git remote to use
       display_fetch_size (bool): if True, run `git count-objects` before and
         after fetch and display delta. Adds two more steps. Defaults to False.
       file_name (str): optional path to a single file to checkout.
       submodule_update_recursive (bool): if True, updates submodules
           recursively.
+
+    Returns: If set_got_revision is True and the checkout was successful, this

[dnj, 2016/02/12 21:54:45]

Why not always return it, even if set_got_revision is not True?

+      returns the commit hash of the checked-out-repo. Otherwise this returns
+      None.
     """
+    retVal = None
+
     # TODO(robertocn): Break this function and refactor calls to it.
     #     The problem is that there are way too many unrealated use cases for
     #     it, and the function's signature is getting unwieldy and its body
     #     unreadable.
     display_fetch_size = display_fetch_size or False
     if not dir_path:
       dir_path = url.rsplit('/', 1)[-1]
       if dir_path.endswith('.git'):  # ex: https://host/foobar.git
         dir_path = dir_path[:-len('.git')]
 
@@ skipping 95 matching lines @@
 
     if set_got_revision:
       rev_parse_step = self('rev-parse', 'HEAD',
                            cwd=dir_path,
                            name='set got_revision',
                            stdout=self.m.raw_io.output(),
                            can_fail_build=False)
 
       if rev_parse_step.presentation.status == 'SUCCESS':
         sha = rev_parse_step.stdout.strip()
+        retVal = sha
         rev_parse_step.presentation.properties['got_revision'] = sha
 
     clean_args = list(itertools.chain(
         *[('-e', path) for path in keep_paths or []]))
 
     self('clean', '-f', '-d', '-x', *clean_args,
       name='git clean%s' % step_suffix,
       cwd=dir_path,
       can_fail_build=can_fail_build)
 
     if submodules:
       self('submodule', 'sync',
         name='submodule sync%s' % step_suffix,
         cwd=dir_path,
         can_fail_build=can_fail_build)
       submodule_update = ['submodule', 'update', '--init']
       if submodule_update_recursive:
         submodule_update.append('--recursive')
       if submodule_update_force:
         submodule_update.append('--force')
       self(*submodule_update,
         name='submodule update%s' % step_suffix,
         cwd=dir_path,
         can_fail_build=can_fail_build)
 
+    return retVal
+
   def get_timestamp(self, commit='HEAD', test_data=None, **kwargs):
     """Find and return the timestamp of the given commit."""
     step_test_data = None
     if test_data is not None:
       step_test_data = lambda: self.m.raw_io.test_api.stream_output(test_data)
     return self('show', commit, '--format=%at', '-s',
                 stdout=self.m.raw_io.output(),
                 step_test_data=step_test_data).stdout.rstrip()
 
   def rebase(self, name_prefix, branch, dir_path, remote_name=None,
@@ skipping 46 matching lines @@
 
     Args:
       bundle_path (Path): The path of the output bundle.
       refs (list): The list of refs to include in the bundle. If None, all
           refs in the Git checkout will be bundled.
       kwargs: Forwarded to '__call__'.
     """
     if not rev_list_args:
       rev_list_args = ['--all']
     self('bundle', 'create', bundle_path, *rev_list_args, **kwargs)