Revert of Revert "Add (another) argument to break git locks in gclient." (patchset #1 id:1 of https://codereview.chromium.org/1865403003/ )

Reason for revert:
This revert breaks /everything/

Original issue's description:
> Revert "Add (another) argument to break git locks in gclient."
> 
> This reverts commit 51797b1d8f.
> 
> BUG=601564
> TBR=iannucci,dpranke,estaab,pgervais
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=299771

TBR=dpranke@google.com,estaab@chromium.org,pgervais@chromium.org,smut@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=601564

Review URL: https://codereview.chromium.org/1867843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299773 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -2050,6 +2050,11 @@ def CMDsync(parser, args):
                     help='Don\'t bootstrap from Google Storage.')
   parser.add_option('--ignore_locks', action='store_true',
                     help='GIT ONLY - Ignore cache locks.')
+  parser.add_option('--break_repo_locks', action='store_true',
+                    help='GIT ONLY - Forcibly remove repo locks (e.g. '
+                      'index.lock). This should only be used if you know for '
+                      'certain that this invocation of gclient is the only '
+                      'thing operating on the git repos (e.g. on a bot).')
   parser.add_option('--lock_timeout', type='int', default=5000,
                     help='GIT ONLY - Deadline (in seconds) to wait for git '
                          'cache lock to become available. Default is %default.')

gclient_scm.py

@@ -327,6 +327,27 @@ class GitWrapper(SCMWrapper):
           os.remove(disabled_hook_path)
         os.rename(os.path.join(hook_dir, f), disabled_hook_path)
 
+  def _maybe_break_locks(self, options):
+    """This removes all .lock files from this repo's .git directory, if the
+    user passed the --break_repo_locks command line flag.
+
+    In particular, this will cleanup index.lock files, as well as ref lock
+    files.
+    """
+    if options.break_repo_locks:
+      git_dir = os.path.join(self.checkout_path, '.git')
+      for path, _, filenames in os.walk(git_dir):
+        for filename in filenames:
+          if filename.endswith('.lock'):
+            to_break = os.path.join(path, filename)
+            self.Print('breaking lock: %s' % (to_break,))
+            try:
+              os.remove(to_break)
+            except OSError as ex:
+              self.Print('FAILED to break lock: %s: %s' % (to_break, ex))
+              raise
+
+
   def update(self, options, args, file_list):
     """Runs git to update or transparently checkout the working copy.
 
@@ -433,6 +454,8 @@ class GitWrapper(SCMWrapper):
       self.Print('________ unmanaged solution; skipping %s' % self.relpath)
       return self._Capture(['rev-parse', '--verify', 'HEAD'])
 
+    self._maybe_break_locks(options)
+
     if mirror:
       self._UpdateMirror(mirror, options)
 

tests/gclient_scm_test.py

@@ -133,6 +133,7 @@ class BaseGitWrapperTestCase(GCBaseTestCase, StdoutCheck, TestCaseUtils,
       self.cache_dir = None
       self.merge = False
       self.jobs = 1
+      self.break_repo_locks = False
       self.delete_unversioned_trees = False
 
   sample_git_import = """blob
@@ -501,6 +502,36 @@ class ManagedGitWrapperTestCase(BaseGitWrapperTestCase):
     sys.stdout.getvalue()
     sys.stdout.close()
 
+  def testUpdateLocked(self):
+    if not self.enabled:
+      return
+    options = self.Options()
+    scm = gclient_scm.CreateSCM(url=self.url, root_dir=self.root_dir,
+                                relpath=self.relpath)
+    file_path = join(self.base_path, '.git', 'index.lock')
+    with open(file_path, 'w'):
+      pass
+    with self.assertRaisesRegexp(subprocess2.CalledProcessError,
+                                 'Unable to create.*/index.lock'):
+      scm.update(options, (), [])
+    sys.stdout.close()
+
+  def testUpdateLockedBreak(self):
+    if not self.enabled:
+      return
+    options = self.Options()
+    options.break_repo_locks = True
+    scm = gclient_scm.CreateSCM(url=self.url, root_dir=self.root_dir,
+                                relpath=self.relpath)
+    file_path = join(self.base_path, '.git', 'index.lock')
+    with open(file_path, 'w'):
+      pass
+    scm.update(options, (), [])
+    self.assertRegexpMatches(sys.stdout.getvalue(),
+                             "breaking lock.*\.git/index\.lock")
+    self.assertFalse(os.path.exists(file_path))
+    sys.stdout.close()
+
   def testUpdateConflict(self):
     if not self.enabled:
       return
@@ -542,6 +573,7 @@ class ManagedGitWrapperTestCaseMox(BaseTestCase):
       self.force = force
       self.reset = False
       self.nohooks = False
+      self.break_repo_locks = False
       # TODO(maruel): Test --jobs > 1.
       self.jobs = 1