Allow gclient sync to overwrite untracked files when moving detached git HEAD.

gclient_scm.py

 # Copyright (c) 2012 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.
 
 """Gclient-specific SCM-specific operations."""
 
 from __future__ import print_function
 
 import errno
 import logging
@@ skipping 468 matching lines @@
         target = upstream_branch
       self._Run(['reset', '--hard', target], options)
 
     if current_type == 'detached':
       # case 0
       self._CheckClean(rev_str)
       self._CheckDetachedHead(rev_str, options)
       if self._Capture(['rev-list', '-n', '1', 'HEAD']) == revision:
         self.Print('Up-to-date; skipping checkout.')
       else:
-        self._Capture(['checkout', '--quiet', '%s' % revision])
+        # 'git checkout' may need to overwrite existing untracked files. Allow
+        # it only when nuclear options are enabled.
+        if options.force and options.delete_unversioned_trees:

[Vadim Sh., 2014/06/20 06:46:46]

The more natural combination would be "--force --reset", but 'gclient sync' step
on bots is not using --reset, and enabling --reset there would make it a lot
slower (I think). So I choose less natural combination of '--force
--delete_unversioned_trees' that's already passed by gclient sync step.

In some sense force git checkout does delete unversioned trees... sort of.

+          self._Capture(['checkout', '--force', '--quiet', '%s' % revision])
+        else:
+          self._Capture(['checkout', '--quiet', '%s' % revision])
       if not printed_path:
         self.Print('_____ %s%s' % (self.relpath, rev_str), timestamp=False)
     elif current_type == 'hash':
       # case 1
       if scm.GIT.IsGitSvn(self.checkout_path) and upstream_branch is not None:
         # Our git-svn branch (upstream_branch) is our upstream
         self._AttemptRebase(upstream_branch, files, options,
                             newbase=revision, printed_path=printed_path,
                             merge=options.merge)
         printed_path = True
@@ skipping 989 matching lines @@
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'theirs-conflict'))
     elif options.manually_grab_svn_rev:
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'postpone'))
     elif command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
       new_command.extend(('--accept', 'postpone'))
     return new_command