Abort git tools if git repo has too many local branches.

git_common.py

 # 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.
 
 # Monkeypatch IMapIterator so that Ctrl-C can kill everything properly.
 # Derived from https://gist.github.com/aljungberg/626518
 import multiprocessing.pool
 from multiprocessing.pool import IMapIterator
 def wrapper(func):
   def wrap(self, timeout=None):
     return func(self, timeout=timeout or 1e100)
   return wrap
 IMapIterator.next = wrapper(IMapIterator.next)
 IMapIterator.__next__ = IMapIterator.next
 # TODO(iannucci): Monkeypatch all other 'wait' methods too.
 
 
 import binascii
 import collections
 import contextlib
 import functools
 import logging
 import os
 import re
 import signal
 import sys
 import tempfile
+import textwrap
 import threading
 
 import subprocess2
 
 
 GIT_EXE = 'git.bat' if sys.platform.startswith('win') else 'git'
 TEST_MODE = False
 
 FREEZE = 'FREEZE'
 FREEZE_SECTIONS = {
@@ skipping 194 matching lines @@
   try:
     reg = re.compile(r'^branch\.(.*)\.%s$' % option)
     lines = run('config', '--get-regexp', reg.pattern).splitlines()
     return {reg.match(k).group(1): v for k, v in (l.split() for l in lines)}
   except subprocess2.CalledProcessError:
     return {}
 
 
 def branches(*args):
   NO_BRANCH = ('* (no branch', '* (detached from ')
-  for line in run('branch', *args).splitlines():
+
+  key = 'depot-tools.branch-limit'
+  limit = 20
+  try:
+    limit = int(config(key, limit))
+  except ValueError:
+    pass
+
+  raw_branches = run('branch', *args).splitlines()
+
+  num = len(raw_branches)
+  if num > limit:
+    print >> sys.stderr, textwrap.dedent("""\
+    Your git repo has too many branches (%d/%d) for this tool to work well.
+
+    You may adjust this limit by running:
+      git config %s <new_limit>
+    """ % (num, limit, key))
+    sys.exit(1)
+
+  for line in raw_branches:
     if line.startswith(NO_BRANCH):
       continue
     yield line.split()[-1]
 
 
 def run_with_retcode(*cmd, **kwargs):
   """Run a command but only return the status code."""
   try:
     run(*cmd, **kwargs)
     return 0
@@ skipping 376 matching lines @@
     return None
   return ret
 
 
 def upstream(branch):
   try:
     return run('rev-parse', '--abbrev-ref', '--symbolic-full-name',
                branch+'@{upstream}')
   except subprocess2.CalledProcessError:
     return None