Gclient with git cache: delete conflicting mirror.

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 443 matching lines @@
       if not (options.force or options.reset):
         # Make sure it's clean
         self._CheckClean(rev_str)
       # Switch over to the new upstream
       self._Run(['remote', 'set-url', self.remote, url], options)
       if mirror:
         with open(os.path.join(
             self.checkout_path, '.git', 'objects', 'info', 'alternates'),
             'w') as fh:
           fh.write(os.path.join(url, 'objects'))
+      self._EnsureValidHeadObjectOrCheckout(revision, options, url)
       self._FetchAndReset(revision, file_list, options)
+
       return_early = True
+    else:
+      self._EnsureValidHeadObjectOrCheckout(revision, options, url)
 
     if return_early:
       return self._Capture(['rev-parse', '--verify', 'HEAD'])
 
     cur_branch = self._GetCurrentBranch()
 
     # Cases:
     # 0) HEAD is detached. Probably from our initial clone.
     #   - make sure HEAD is contained by a named ref, then update.
     # Cases 1-4. HEAD is a branch.
@@ skipping 556 matching lines @@
       # whitespace between projects when syncing.
       self.Print('')
 
   @staticmethod
   def _CheckMinVersion(min_version):
     (ok, current_version) = scm.GIT.AssertVersion(min_version)
     if not ok:
       raise gclient_utils.Error('git version %s < minimum required %s' %
                                 (current_version, min_version))
 
+  def _EnsureValidHeadObjectOrCheckout(self, revision, options, url):
+    # Special case handling if all 3 conditions are met:
+    #   * the mirros have recently changed, but deps destination remains same,
+    #   * the git histories of mirrors are conflicting.
+    #   * git cache is used
+    # This manifests itself in current checkout having invalid HEAD commit on
+    # most git operations. Since git cache is used, just deleted the .git
+    # folder, and re-create it by cloning.
+    try:
+      self._Capture(['rev-list', '-n', '1', 'HEAD'])
+    except subprocess2.CalledProcessError as e:
+      if ('fatal: bad object HEAD' in e.stderr

[Ryan Tseng, 2015/08/24 22:40:46]

This sort of error detection scares me :/.  Theres no way to know if it'll carry
over from version to verison.

though failing to run rev-list on HEAD should be signal enough that HEAD is
broken somehow?

[tandrii(chromium), 2015/08/25 08:00:52]

So, I thought this way:

best case -> it works
ok case -> the error changes, so our waterfall gets red. Oh well, not any worse
than now.
worst case -> the error is same, but for some other weird reason. Then we'll mv
.git to _bad_scm, even though we didn't have to. Still tolerable.

+          and self.cache_dir and self.cache_dir in url):
+        self.Print((
+          'Likely due to DEPS change with git cache_dir, '
+          'the current commit points to no longer existing object.\n'
+          '%s' % e)
+        )
+        self._DeleteOrMove(options.force)
+        self._Clone(revision, url, options)
+      else:
+        raise
+
   def _IsRebasing(self):
     # Check for any of REBASE-i/REBASE-m/REBASE/AM. Unfortunately git doesn't
     # have a plumbing command to determine whether a rebase is in progress, so
     # for now emualate (more-or-less) git-rebase.sh / git-completion.bash
     g = os.path.join(self.checkout_path, '.git')
     return (
       os.path.isdir(os.path.join(g, "rebase-merge")) or
       os.path.isdir(os.path.join(g, "rebase-apply")))
 
   def _CheckClean(self, rev_str):
@@ skipping 602 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