Add a --keep-going flag for people who run rebase-update infrequently.

git_rebase_update.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """
 Tool to update all branches to have the latest changes from their upstreams.
 """
 
 import argparse
@@ skipping 178 matching lines @@
 
   git.remove_merge_base(branch)
   git.get_or_create_merge_base(branch)
 
   return True
 
 
 def main(args=None):
   parser = argparse.ArgumentParser()
   parser.add_argument('--verbose', '-v', action='store_true')
+  parser.add_argument('--keep-going', '-k', action='store_true',
+                      help='Keep processing past failed rebases.')
   parser.add_argument('--no_fetch', '--no-fetch', '-n',
                       action='store_true',
                       help='Skip fetching remotes.')
   opts = parser.parse_args(args)
 
   if opts.verbose:  # pragma: no cover
     logging.getLogger().setLevel(logging.DEBUG)
 
   # TODO(iannucci): snapshot all branches somehow, so we can implement
   #                 `git rebase-update --undo`.
@@ skipping 29 matching lines @@
     fetch_remotes(branch_tree)
 
   merge_base = {}
   for branch, parent in branch_tree.iteritems():
     merge_base[branch] = git.get_or_create_merge_base(branch, parent)
 
   logging.debug('branch_tree: %s' % pformat(branch_tree))
   logging.debug('merge_base: %s' % pformat(merge_base))
 
   retcode = 0
+  unrebased_branches = []
   # Rebase each branch starting with the root-most branches and working
   # towards the leaves.
   for branch, parent in git.topo_iter(branch_tree):
     if git.is_dormant(branch):
       print 'Skipping dormant branch', branch
     else:
       ret = rebase_branch(branch, parent, merge_base[branch])
       if not ret:
         retcode = 1
-        break
+
+        if opts.keep_going:
+          print '--keep-going set, continuing with next branch.'
+          unrebased_branches.append(branch)
+          if git.in_rebase():
+            git.run_with_retcode('rebase', '--abort')
+          if git.in_rebase():  # pragma: no cover
+            print 'Failed to abort rebase. Something is really wrong.'
+            break
+        else:
+          break
+
+  if unrebased_branches:
+    print
+    print 'The following branches could not be cleanly rebased:'
+    for branch in unrebased_branches:
+      print '  %s' % branch
 
   if not retcode:
     remove_empty_branches(branch_tree)
 
     # return_branch may not be there any more.
     if return_branch in git.branches():
       git.run('checkout', return_branch)
       git.thaw()
     else:
       root_branch = git.root()
@@ skipping 10 matching lines @@
 
   return retcode
 
 
 if __name__ == '__main__':  # pragma: no cover
   try:
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)