Add a revert script.

tools/revert.py

Index: tools/revert.py
===================================================================
--- tools/revert.py	(revision 0)
+++ tools/revert.py	(revision 0)
@@ -0,0 +1,193 @@
+#!/usr/bin/python
+
+# Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+import optparse
+import os
+import platform
+import subprocess
+import sys
+
+"""A script used to revert one or a sequence of consecutive CLs, for svn and
+git-svn users.
+"""
+
+def parse_args():
+  parser = optparse.OptionParser()
+  parser.add_option('--revisions', '-r', dest='rev_range', action='store',
+                    default=None, help='The revision number(s) of the commits '
+                    'you wish to undo. An individual number, or a range (8-10, '
+                    '8..10, or 8:10).')
+  args, _ = parser.parse_args()
+  revision_range = args.rev_range
+  if revision_range == None:
+    maybe_fail('You must specify at least one revision number to revert.')
+  if revision_range.find('-') > -1 or revision_range.find(':') > -1 or \
+      revision_range.find('..') > -1:
+    # We have a range of commits to revert.
+    split = revision_range.split('-')
+    if len(split) == 1:
+      split = revision_range.split(':')
+    if len(split) == 1:
+      split = revision_range.split('..')
+    start = int(split[0])
+    end = int(split[1])
+    if start > end:
+      temp = start
+      start = end
+      end = temp
+    if start != end:
+      maybe_fail('Warning: Are you sure you want to revert a range of '
+                 'revisions? If you just want to revert one CL, only specify '
+                 'one revision number.', user_input=True)
+  else:
+    start = end = int(revision_range)
+  return start, end
+
+def maybe_fail(msg, user_input=False):
+  """Determine if we have encountered a condition upon which our script cannot
+  continue, and abort if so.
+  Args:
+    - msg: The error or user prompt message to print.
+    - user_input: True if we require user confirmation to continue. We assume
+                  that the user must enter y to proceed.
+  """
+  if user_input:
+    force = raw_input(msg + ' (y/N) ')
+    if force != 'y':
+      sys.exit(0)
+  else:
+    print msg
+    sys.exit(1)
+
+def has_new_code(is_git):
+  """Tests if there are any newer versions of files on the server.
+  Args:
+    - is_git: True if we are working in a git repository.
+  """
+  os.chdir(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+  if not is_git:
+    results, _ = run_cmd(['svn', 'st'])
+  else:
+    results, _ = run_cmd(['git', 'status'])
+  for line in results.split('\n'):
+    if not is_git and (not line.strip().startswith('?') and line != ''):
+      return True
+    elif is_git and ('Changes to be committed' in line or 
+        'Changes not staged for commit:' in line):
+      return True
+  if is_git:
+    p = subprocess.Popen(['git', 'log', '-1'], stdout=subprocess.PIPE)
+    output, _ = p.communicate()
+    if find_git_info(output) == None:
+      return True
+  return False
+
+def run_cmd(cmd_list, suppress_output=False, std_in=''):
+  """Run the specified command and print out any output to stdout."""
+  print ' '.join(cmd_list)
+  p = subprocess.Popen(cmd_list, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                       stdin=subprocess.PIPE,
+                       shell=(platform.system()=='Windows'))
+  output, stderr = p.communicate(std_in)
+  if output and not suppress_output:
+    print output
+  if stderr and not suppress_output:
+    print stderr
+  return (output, stderr)
+
+def runs_git():
+  """Returns True if we're standing in an svn-git repository."""
+  p = subprocess.Popen(['svn', 'info'], stdout=subprocess.PIPE,
+                       stderr=subprocess.PIPE)
+  output, err = p.communicate()
+  if err != None and 'is not a working copy' in err:
+    p = subprocess.Popen(['git', 'status'], stdout=subprocess.PIPE)
+    output, _ = p.communicate()
+    if 'fatal: Not a git repository' in output:
+      maybe_fail('Error: not running git or svn.')
+    else:
+      return True
+  return False
+
+def find_git_info(git_log, rev_num=None):
+  """Determine the latest svn revision number if rev_num = None, or find the 
+  git commit_id that corresponds to a particular svn revision number.
+  """
+  for line in git_log.split('\n'):
+    tokens = line.split()
+    if len(tokens) == 2 and tokens[0] == 'commit':
+      current_commit_id = tokens[1]
+    elif len(tokens) > 0 and tokens[0] == 'git-svn-id:':
+      revision_number = int(tokens[1].split('@')[1])
+      if revision_number == rev_num:
+        return current_commit_id
+      if rev_num == None:
+        return revision_number
+
+def revert(start, end, is_git):
+  """Revert the sequence of CLs.
+  Args:
+    - start: The first CL to revert.
+    - end: The last CL to revert.
+    - is_git: True if we are in a git-svn checkout.
+  """
+  if not is_git:
+    _, err = run_cmd(['svn', 'merge', '-r', '%d:%d' % (end, start-1), '.'],
+                     std_in='p')
+    if 'Conflict discovered' in err:
+      maybe_fail('Please fix the above conflicts before submitting. Then create'
+             ' a CL and submit your changes to complete the revert.')
+
+  else:
+    # If we're running git, we have to use the log feature to find the commit
+    # id(s) that correspond to the particular revision number(s).
+    output, _ = run_cmd(['git', 'log', '-1'], suppress_output=True)
+    current_revision = find_git_info(output)
+    distance = (current_revision-start) + 1
+    output, _ = run_cmd(['git', 'log', '-%d' % distance], suppress_output=True)
+    reverts = [start]
+    commit_msg = '"Reverting %d"' % start
+    if end != start:
+      reverts = range(start, end + 1)
+      reverts.reverse()
+      commit_msg = '%s-%d"' % (commit_msg[:-1], end)
+    for revert in reverts:
+      git_commit_id = find_git_info(output, revert)
+      if git_commit_id == None:
+        maybe_fail('Error: Revision number not found. Is this earlier than your'
+                   ' git checkout history?')
+      _, err = run_cmd(['git', 'revert', '-n', git_commit_id])
+      if 'error: could not revert' in err or 'unmerged' in err:
+        command_sequence = ''
+        for revert in reverts:
+          git_commit_id = find_git_info(output, revert)
+          command_sequence += 'git revert -n %s\n' % git_commit_id
+        maybe_fail('There are conflicts while reverting. Please resolve these '
+                   'after manually running:\n' + command_sequence + 'and then '
+                   'create a CL and submit to complete the revert.')
+    run_cmd(['git', 'commit', '-m', commit_msg])
+
+def main():
+  revisions = parse_args()
+  git_user = runs_git()
+  if has_new_code(git_user):
+    if git_user:
+      maybe_fail('Your tree has local modifications! Move to a clean tree and '
+          'try running this script again.')
+    else:
+      maybe_fail('WARNING: This checkout has local modifications!! This could '
+           'result in a CL that is not just a revert and/or you could lose your'
+           ' local changes! Are you **SURE** you want to continue? ',
+         user_input=True)
+  if git_user:
+    run_cmd(['git', 'cl', 'rebase'])
+  run_cmd(['gclient', 'sync'])
+  revert(revisions[0], revisions[1], git_user)
+  print ('Now, create a CL and submit! The buildbots and your teammates thank '
+         'you!')
+
+if __name__ == '__main__':
+  main()