Improve "dcommit in git repo" error message.

git_auto_svn.py

Index: git_auto_svn.py
diff --git a/git_auto_svn.py b/git_auto_svn.py
index 0e8f341c7ca616c50cd7e3a75a1f0b3af0981640..c1266f8b502c46afe0199bb592a5229c45ca81b3 100755
--- a/git_auto_svn.py
+++ b/git_auto_svn.py
@@ -50,6 +50,19 @@ def run_svn(*cmd, **kwargs):
   return ret, err
 
 
+def get_footer_svn_id(branch=None):
+  if not branch:
+    branch = root()
+  svn_id = None
+  message = run_git('log', '-1', '--format=%B', branch)
+  footers = parse_footers(message)
+  git_svn_id = get_unique(footers, 'git-svn-id')
+  match = GIT_SVN_ID_PATTERN.match(git_svn_id)
+  if match:
+    svn_id = match.group(1)
+  return svn_id
+
+
 def main(argv):
   # No command line flags. Just use the parser to prevent people from trying
   # to pass flags that don't do anything, and to provide 'usage'.
@@ -58,14 +71,11 @@ def main(argv):
   parser.parse_args(argv)
 
   upstream = root()
-  message = run_git('log', '-1', '--format=%B', upstream)
-  footers = parse_footers(message)
-  git_svn_id = get_unique(footers, 'git-svn-id')
-  match = GIT_SVN_ID_PATTERN.match(git_svn_id)
-  assert match, 'No valid git-svn-id footer found on %s.' % upstream
-  print 'Found git-svn-id footer %s on %s' % (match.group(1), upstream)
+  svn_id = get_footer_svn_id(upstream)
+  assert svn_id, 'No valid git-svn-id footer found on %s.' % upstream
+  print 'Found git-svn-id footer %s on %s' % (svn_id, upstream)
 
-  parsed_svn = urlparse.urlparse(match.group(1))
+  parsed_svn = urlparse.urlparse(svn_id)
   path_components = parsed_svn.path.split('/')
   svn_repo = None
   svn_path = None
@@ -86,7 +96,7 @@ def main(argv):
                ' from https://chromium-access.appspot.com' % maybe_repo)
         print
       continue
-  assert svn_repo is not None, 'Unable to find svn repo for %s' % match.group(1)
+  assert svn_repo is not None, 'Unable to find svn repo for %s' % svn_id
   print 'Found upstream svn repo %s and path %s' % (svn_repo, svn_path)
 
   set_config('svn-remote.svn.url', svn_repo)