hooks/pre_push

#!/usr/bin/env python
# Copyright 2015 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 sys
import subprocess

"""Detect forced pushes (on the client) and prompt the user before going on."""


def read_from_tty():
  try:
    import posix  # No way to do this on Windows, just give up there.
    with open('/dev/tty') as tty_fd:
      return tty_fd.readline().strip()
  except:
    return None


def Main():
  # Allow force pushes in repos forked elsewhere (e.g. googlesource).
  remote_url = sys.argv[2] if len(sys.argv) >= 2 else ''
  if 'github.com' not in remote_url:
    return 0

  parts = sys.stdin.readline().split()
  if len(parts) < 4:
    return 0
  local_ref, local_sha, remote_ref, remote_sha = parts
  cmd = ['git', 'rev-list', '--count', remote_sha, '--not', local_sha,
         '--max-count=1']

  is_force_push = '0'
  try:
    is_force_push = subprocess.check_output(cmd).strip()
  except(subprocess.CalledProcessError):
    return 0

  if is_force_push != '0':
    sys.stderr.write('\033[31mWARNING: Force pushing will break the ' +
                     'github.com -> googlesource.com mirroring.\033[0m\n' +
                     'This is almost certainly a bad idea.\n')

    sys.stderr.write('Type y to continue: ')
    if read_from_tty() != 'y':
      return 1

  return 0


if __name__ == '__main__':
  sys.exit(Main())