Add a family of git-commands to assist with the management of multiple CLs/branches.

git-rebase-update - ensure all branches are up to date
git-new-branch - create branches
git-rename-branch - rename a branch while preserving parentage relationships
git-reparent-branch - change the parent of a branch, including rebasing it correctly onto that new parent.
git-squash-branch - collapse a branch into a single commit
git-upstream-diff - show the diff between the current branch and it's upstream branch
git-mark-merge-base - explicitly set what you want the above tools to consider the merge-base for the current branch.

R=agable@chromium.org, hinoka@chromium.org, stip@chromium.org, szager@chromium.org
BUG=261738

Review URL: https://codereview.chromium.org/184253003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@259520 0039d316-1c4b-4281-b951-d872f2087c98

git_rename_branch.py

@@ -0,0 +1,50 @@
+#!/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.
+
+"""Rename the current branch while maintaining correct dependencies."""
+
+import argparse
+import sys
+
+import subprocess2
+
+from git_common import current_branch, run, set_branch_config, branch_config
+from git_common import branch_config_map
+
+def main(args):
+  current = current_branch()
+  if current == 'HEAD':
+    current = None
+  old_name_help = 'The old branch to rename.'
+  if current:
+    old_name_help += ' (default %(default)r)'
+
+  parser = argparse.ArgumentParser()
+  parser.add_argument('old_name', nargs=('?' if current else 1),
+                      help=old_name_help, default=current)
+  parser.add_argument('new_name', help='The new branch name.')
+
+  opts = parser.parse_args(args)
+
+  # when nargs=1, we get a list :(
+  if isinstance(opts.old_name, list):
+    opts.old_name = opts.old_name[0]
+
+  try:
+    run('branch', '-m', opts.old_name, opts.new_name)
+
+    # update the downstreams
+    for branch, merge in branch_config_map('merge').iteritems():
+      if merge == 'refs/heads/' + opts.old_name:
+        # Only care about local branches
+        if branch_config(branch, 'remote') == '.':
+          set_branch_config(branch, 'merge', 'refs/heads/' + opts.new_name)
+  except subprocess2.CalledProcessError as cpe:
+    sys.stderr.write(cpe.stderr)
+    return 1
+
+
+if __name__ == '__main__':  # pragma: no cover
+  sys.exit(main(sys.argv[1:]))