new_contents: #   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  # A script to bisect the mainline commits and find the culprit commit.
  # The default 'git bisect' checks feature branches, which is not desired
  # because commits in feature branch might not pass tests or compile.
  #
  # Example:
  #   python ../bisect.py --git_dir=$PWD/../Paddle --build_dir=$PWD \
  #       --good_commit=3647ed6 --bad_commit=279aa6 \
  #       --test_target=test_rnn_encoder_decoder
  
  import argparse
  import os
  import subprocess
  import sys
  
  parser = argparse.ArgumentParser(description=__doc__)
  parser.add_argument(
      '--git_dir', type=str, default='', help='git repo root directory.')
  parser.add_argument(
      '--build_dir', type=str, default='', help='build directory.')
  parser.add_argument(
      '--good_commit',
      type=str,
      default='',
      help='The old commit known to be good.')
  parser.add_argument(
      '--bad_commit',
      type=str,
      default='',
      help='The new commit known to be bad.')
  parser.add_argument(
      '--test_target', type=str, default='', help='The test target to evaluate.')
  parser.add_argument(
      '--bisect_branch',
      type=str,
      default='develop',
      help='The mainline branch to bisect (feature branch ignored.')
  parser.add_argument(
      '--log_file', type=str, default='', help='The file use to log outputs.')
  parser.add_argument(
      '--test_times',
      type=int,
      default=10,
      help="Number of times to run the test target.")
  parser.add_argument(
      '--build_parallel', type=int, default=32, help="make parallelism.")
  args = parser.parse_args()
  
  if not args.log_file:
      args.log_file = '/tmp/%s...%s.log' % (args.good_commit, args.bad_commit)
  
  
  def print_arguments():
      print('-----------  Configuration Arguments -----------')
      for arg, value in sorted(vars(args).iteritems()):
          print('%s: %s' % (arg, value))
      print('------------------------------------------------')
  
  
  print_arguments()
  
  # List the commits in mainline branch.
  os.chdir(args.git_dir)
  ret = subprocess.check_output(
      [
          'git rev-list --first-parent %s...%s' % (args.good_commit,
                                                   args.bad_commit)
      ],
      shell=True)
  sys.stdout.write('commits found:\n%s\n' % ret)
  commits = ret.strip().split('\n')
  os.chdir(args.build_dir)
  # Clean up previous logs.
  subprocess.check_output(['echo "" > %s' % args.log_file], shell=True)
  
  last_culprit = ''
  while True:
      # Get to the mainline branch and clean up
      os.chdir(args.git_dir)
      subprocess.check_output(
          [
              'git checkout %s && git clean -fd && git checkout .' %
              args.bisect_branch
          ],
          shell=True)
  
      if not commits:
          sys.stdout.write('no commits to bisect\n')
          exit()
      # checkout the picked branch.
      pick_idx = len(commits) / 2
      pick = commits[pick_idx]
      os.chdir(args.git_dir)
      subprocess.check_output(['git checkout %s' % pick], shell=True)
  
      # Clean builds and compile.
      # We assume mainline commits should always compile.
      os.chdir(args.build_dir)
      sys.stdout.write('eval commit %d/%d: %s\n' % (pick_idx, len(commits), pick))
      # Link error can happen without complete clean up.
      cmd = ('rm -rf * && '
             'cmake -DWITH_TESTING=ON %s >> %s && make -j%s >> %s' %
             (args.git_dir, args.log_file, args.build_parallel, args.log_file))
      sys.stdout.write('cmd: %s\n' % cmd)
      try:
          subprocess.check_output([cmd], shell=True)
      except subprocess.CalledProcessError as e:
          sys.stderr.write('failed to build commit: %s\n%s\n' % (pick, e))
          exit()
      # test the selected branch.
      passed = True
      try:
          cmd = ('ctest --repeat-until-fail %s -R %s >> %s' %
                 (args.test_times, args.test_target, args.log_file))
          sys.stdout.write('cmd: %s\n' % cmd)
          subprocess.check_output([cmd], shell=True)
      except subprocess.CalledProcessError as e:
          passed = False
          last_culprit = pick
      sys.stdout.write('eval %s passed: %s\n' % (pick, passed))
      if passed:
          if pick_idx == 0: break
          commits = commits[:pick_idx]
      else:
          if pick_idx + 1 >= len(commits): break
          commits = commits[pick_idx + 1:]
  
  sys.stdout.write('Culprit commit: %s\n' % last_culprit)
  
subject: Add a script to bisect to a culprit commit.