Support merging with conflicts with git-drover.

git_drover.py

 #!/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.
 """git drover: A tool for merging changes to release branches."""
 
 import argparse
+import cPickle
 import functools
 import logging
 import os
 import shutil
 import subprocess
 import sys
 import tempfile
 
 import git_common
 
 
 class Error(Exception):
   pass
 
 
+_PATCH_ERROR_MESSAGE = """Patch failed to apply.
+
+A workdir for this cherry-pick has been created in
+  {0}
+
+To continue, resolve the conflicts there and run
+  git drover --continue {0}
+
+To abort this cherry-pick run
+  git drover --abort {0}
+"""
+
+
+class PatchError(Error):
+  """An error indicating that the patch failed to apply."""
+
+  def __init__(self, workdir):
+    super(PatchError, self).__init__(_PATCH_ERROR_MESSAGE.format(workdir))
+
+
+_DEV_NULL_FILE = open(os.devnull, 'w')
+
 if os.name == 'nt':
   # This is a just-good-enough emulation of os.symlink for drover to work on
   # Windows. It uses junctioning of directories (most of the contents of
   # the .git directory), but copies files. Note that we can't use
   # CreateSymbolicLink or CreateHardLink here, as they both require elevation.
   # Creating reparse points is what we want for the directories, but doing so
   # is a relatively messy set of DeviceIoControl work at the API level, so we
   # simply shell to `mklink /j` instead.
   def emulate_symlink_windows(source, link_name):
     if os.path.isdir(source):
       subprocess.check_call(['mklink', '/j',
                              link_name.replace('/', '\\'),
                              source.replace('/', '\\')],
                             shell=True)
     else:
       shutil.copy(source, link_name)
   mk_symlink = emulate_symlink_windows
 else:
   mk_symlink = os.symlink
 
 
 class _Drover(object):
 
-  def __init__(self, branch, revision, parent_repo, dry_run):
+  def __init__(self, branch, revision, parent_repo, dry_run, verbose):
     self._branch = branch
     self._branch_ref = 'refs/remotes/branch-heads/%s' % branch
     self._revision = revision
     self._parent_repo = os.path.abspath(parent_repo)
     self._dry_run = dry_run
     self._workdir = None
     self._branch_name = None
-    self._dev_null_file = open(os.devnull, 'w')
+    self._needs_cleanup = True
+    self._verbose = verbose
+    self._process_options()
+
+  def _process_options(self):
+    if self._verbose:
+      logging.getLogger().setLevel(logging.DEBUG)
+
+
+  @classmethod
+  def resume(cls, workdir):
+    """Continues a cherry-pick that required manual resolution.
+
+    Args:
+      workdir: A string containing the path to the workdir used by drover.
+    """
+    drover = cls._restore_drover(workdir)
+    drover._continue()
+
+  @classmethod
+  def abort(cls, workdir):
+    """Aborts a cherry-pick that required manual resolution.
+
+    Args:
+      workdir: A string containing the path to the workdir used by drover.
+    """
+    drover = cls._restore_drover(workdir)
+    drover._cleanup()
+
+  @staticmethod
+  def _restore_drover(workdir):
+    """Restores a saved drover state contained within a workdir.
+
+    Args:
+      workdir: A string containing the path to the workdir used by drover.
+    """
+    try:
+      with open(os.path.join(workdir, '.git', 'drover'), 'rb') as f:
+        drover = cPickle.load(f)
+        drover._process_options()
+        return drover
+    except (IOError, cPickle.UnpicklingError):
+      raise Error('%r is not git drover workdir' % workdir)
+
+  def _continue(self):
+    if os.path.exists(os.path.join(self._workdir, '.git', 'CHERRY_PICK_HEAD')):
+      self._run_git_command(
+          ['commit', '--no-edit'],
+          error_message='All conflicts must be resolved before continuing')
+
+    if self._upload_and_land():
+      # Only clean up the workdir on success. The manually resolved cherry-pick
+      # can be reused if the user cancels before landing.
+      self._cleanup()
 
   def run(self):
     """Runs this Drover instance.
 
     Raises:
       Error: An error occurred while attempting to cherry-pick this change.
     """
     try:
       self._run_internal()
     finally:
       self._cleanup()
 
   def _run_internal(self):
     self._check_inputs()
     if not self._confirm('Going to cherry-pick\n"""\n%s"""\nto %s.' % (
         self._run_git_command(['show', '-s', self._revision]), self._branch)):
       return
     self._create_checkout()
-    self._prepare_cherry_pick()
-    if self._dry_run:
-      logging.info('--dry_run enabled; not landing.')
+    self._perform_cherry_pick()
+    self._upload_and_land()
+
+  def _cleanup(self):
+    if not self._needs_cleanup:
       return
 
-    self._run_git_command(['cl', 'upload'],
-                          error_message='Upload failed',
-                          interactive=True)
-
-    if not self._confirm('About to land on %s.' % self._branch):
-      return
-    self._run_git_command(['cl', 'land', '--bypass-hooks'], interactive=True)
-
-  def _cleanup(self):
-    if self._branch_name:
-      try:
-        self._run_git_command(['cherry-pick', '--abort'])
-      except Error:
-        pass
-      self._run_git_command(['checkout', '--detach'])
-      self._run_git_command(['branch', '-D', self._branch_name])
     if self._workdir:
       logging.debug('Deleting %s', self._workdir)
       if os.name == 'nt':
-        # Use rmdir to properly handle the junctions we created.
-        subprocess.check_call(['rmdir', '/s', '/q', self._workdir], shell=True)
+        try:
+          # Use rmdir to properly handle the junctions we created.
+          subprocess.check_call(
+              ['rmdir', '/s', '/q', self._workdir], shell=True)
+        except subprocess.CalledProcessError:
+          logging.error(
+              'Failed to delete workdir %r. Please remove it manually.',
+              self._workdir)
       else:
         shutil.rmtree(self._workdir)
-    self._dev_null_file.close()
+    self._workdir = None
+    if self._branch_name:
+      self._run_git_command(['branch', '-D', self._branch_name])
 
   @staticmethod
   def _confirm(message):
     """Show a confirmation prompt with the given message.
 
     Returns:
       A bool representing whether the user wishes to continue.
     """
     result = ''
     while result not in ('y', 'n'):
@@ skipping 47 matching lines @@
     """
     parent_git_dir = os.path.abspath(self._run_git_command(
         ['rev-parse', '--git-dir']).strip())
     self._workdir = tempfile.mkdtemp(prefix='drover_%s_' % self._branch)
     logging.debug('Creating checkout in %s', self._workdir)
     git_dir = os.path.join(self._workdir, '.git')
     git_common.make_workdir_common(parent_git_dir, git_dir, self.FILES_TO_LINK,
                                    self.FILES_TO_COPY, mk_symlink)
     self._run_git_command(['config', 'core.sparsecheckout', 'true'])
     with open(os.path.join(git_dir, 'info', 'sparse-checkout'), 'w') as f:
-      f.write('codereview.settings')
+      f.write('/codereview.settings')
 
     branch_name = os.path.split(self._workdir)[-1]
     self._run_git_command(['checkout', '-b', branch_name, self._branch_ref])
     self._branch_name = branch_name
 
-  def _prepare_cherry_pick(self):
-    self._run_git_command(['cherry-pick', '-x', self._revision],
-                          error_message='Patch failed to apply')
+  def _perform_cherry_pick(self):
+    try:
+      self._run_git_command(['cherry-pick', '-x', self._revision],
+                            error_message='Patch failed to apply')
+    except Error:
+      self._prepare_manual_resolve()
+      self._save_state()
+      self._needs_cleanup = False
+      raise PatchError(self._workdir)
+
+  def _save_state(self):
+    """Saves the state of this Drover instances to the workdir."""
+    with open(os.path.join(self._workdir, '.git', 'drover'), 'wb') as f:
+      cPickle.dump(self, f)
+
+  def _prepare_manual_resolve(self):
+    """Prepare the workdir for the user to manually resolve the cherry-pick."""
+    # Files that have been deleted between branch and cherry-pick will not have
+    # their skip-worktree bit set so set it manually for those files to avoid
+    # git status incorrectly listing them as unstaged deletes.
+    repo_status = self._run_git_command(['status', '--porcelain']).splitlines()
+    extra_files = [f[3:] for f in repo_status if f[:2] == ' D']
+    if extra_files:
+      self._run_git_command(['update-index', '--skip-worktree', '--'] +
+                            extra_files)
+
+  def _upload_and_land(self):
+    if self._dry_run:
+      logging.info('--dry_run enabled; not landing.')
+      return True
+
     self._run_git_command(['reset', '--hard'])
+    self._run_git_command(['cl', 'upload'],
+                          error_message='Upload failed',
+                          interactive=True)
+
+    if not self._confirm('About to land on %s.' % self._branch):
+      return False
+    self._run_git_command(['cl', 'land', '--bypass-hooks'], interactive=True)
+    return True
 
   def _run_git_command(self, args, error_message=None, interactive=False):
     """Runs a git command.
 
     Args:
       args: A list of strings containing the args to pass to git.
-      interactive:
       error_message: A string containing the error message to report if the
           command fails.
+      interactive: A bool containing whether the command requires user
+          interaction. If false, the command will be provided with no input and
+          the output is captured.
 
     Raises:
       Error: The command failed to complete successfully.
     """
     cwd = self._workdir if self._workdir else self._parent_repo
     logging.debug('Running git %s (cwd %r)', ' '.join('%s' % arg
                                                       for arg in args), cwd)
 
     run = subprocess.check_call if interactive else subprocess.check_output
 
+    # Discard stderr unless verbose is enabled.
+    stderr = None if self._verbose else _DEV_NULL_FILE
+
     try:
-      return run(['git'] + args,
-                 shell=False,
-                 cwd=cwd,
-                 stderr=self._dev_null_file)
+      return run(['git'] + args, shell=False, cwd=cwd, stderr=stderr)
     except (OSError, subprocess.CalledProcessError) as e:
       if error_message:
         raise Error(error_message)
       else:
         raise Error('Command %r failed: %s' % (' '.join(args), e))
 
 
-def cherry_pick_change(branch, revision, parent_repo, dry_run):
+def cherry_pick_change(branch, revision, parent_repo, dry_run, verbose=False):
   """Cherry-picks a change into a branch.
 
   Args:
     branch: A string containing the release branch number to which to
         cherry-pick.
     revision: A string containing the revision to cherry-pick. It can be any
         string that git-rev-parse can identify as referring to a single
         revision.
     parent_repo: A string containing the path to the parent repo to use for this
         cherry-pick.
-    dry_run: A boolean containing whether to stop before uploading the
+    dry_run: A bool containing whether to stop before uploading the
         cherry-pick cl.
+    verbose: A bool containing whether to print verbose logging.
 
   Raises:
     Error: An error occurred while attempting to cherry-pick |cl| to |branch|.
   """
-  drover = _Drover(branch, revision, parent_repo, dry_run)
+  drover = _Drover(branch, revision, parent_repo, dry_run, verbose)
   drover.run()
 
 
+def continue_cherry_pick(workdir):
+  """Continues a cherry-pick that required manual resolution.
+
+  Args:
+    workdir: A string containing the path to the workdir used by drover.
+  """
+  _Drover.resume(workdir)
+
+
+def abort_cherry_pick(workdir):
+  """Aborts a cherry-pick that required manual resolution.
+
+  Args:
+    workdir: A string containing the path to the workdir used by drover.
+  """
+  _Drover.abort(workdir)
+
+
 def main():
   parser = argparse.ArgumentParser(
       description='Cherry-pick a change into a release branch.')
+  group = parser.add_mutually_exclusive_group(required=True)
   parser.add_argument(
       '--branch',
       type=str,
-      required=True,
       metavar='<branch>',
       help='the name of the branch to which to cherry-pick; e.g. 1234')
-  parser.add_argument('--cherry-pick',
-                      type=str,
-                      required=True,
-                      metavar='<change>',
-                      help=('the change to cherry-pick; this can be any string '
-                            'that unambiguously refers to a revision'))
+  group.add_argument(
+      '--cherry-pick',
+      type=str,
+      metavar='<change>',
+      help=('the change to cherry-pick; this can be any string '
+            'that unambiguously refers to a revision not involving HEAD'))
+  group.add_argument(
+      '--continue',
+      type=str,
+      nargs='?',
+      dest='resume',
+      const=os.path.abspath('.'),
+      metavar='path_to_workdir',
+      help='Continue a drover cherry-pick after resolving conflicts')
+  group.add_argument('--abort',
+                     type=str,
+                     nargs='?',
+                     const=os.path.abspath('.'),
+                     metavar='path_to_workdir',
+                     help='Abort a drover cherry-pick')
   parser.add_argument(
       '--parent_checkout',
       type=str,
       default=os.path.abspath('.'),
       metavar='<path_to_parent_checkout>',
       help=('the path to the chromium checkout to use as the source for a '
             'creating git-new-workdir workdir to use for cherry-picking; '
             'if unspecified, the current directory is used'))
   parser.add_argument(
       '--dry-run',
       action='store_true',
       default=False,
       help=("don't actually upload and land; "
             "just check that cherry-picking would succeed"))
   parser.add_argument('-v',
                       '--verbose',
                       action='store_true',
                       default=False,
                       help='show verbose logging')
   options = parser.parse_args()
-  if options.verbose:
-    logging.getLogger().setLevel(logging.DEBUG)
   try:
-    cherry_pick_change(options.branch, options.cherry_pick,
-                       options.parent_checkout, options.dry_run)
+    if options.resume:
+      _Drover.resume(options.resume)
+    elif options.abort:
+      _Drover.abort(options.abort)
+    else:
+      if not options.branch:
+        parser.error('argument --branch is required for --cherry-pick')
+      cherry_pick_change(options.branch, options.cherry_pick,
+                         options.parent_checkout, options.dry_run,
+                         options.verbose)
   except Error as e:
-    logging.error(e.message)
+    print 'Error:', e.message
     sys.exit(128)
 
 
 if __name__ == '__main__':
   main()