Remove git lockfile flakiness on win (bot_update)

Hypothesis: Sometimes bot update fails because windows fails to delete
a lockfile associated with a git process.

Test: If this happens, let's delete that lockfile and try again.

BUG=651602

Review-Url: https://codereview.chromium.org/2382653005

recipe_modules/bot_update/resources/bot_update.py

@@ -322,7 +322,7 @@ def gclient_configure(solutions, target_os, target_os_only, git_cache_dir):
         solutions, target_os, target_os_only, git_cache_dir))
 
 
-def gclient_sync(with_branch_heads, shallow):
+def gclient_sync(with_branch_heads, shallow, break_repo_locks):
   # We just need to allocate a filename.
   fd, gclient_output_file = tempfile.mkstemp(suffix='.json')
   os.close(fd)
@@ -334,6 +334,8 @@ def gclient_sync(with_branch_heads, shallow):
     cmd += ['--with_branch_heads']
   if shallow:
     cmd += ['--shallow']
+  if break_repo_locks:
+    cmd += ['--break_repo_locks']
 
   try:
     call(*cmd, tries=1)
@@ -753,10 +755,14 @@ def ensure_checkout(solutions, revisions, first_sln, target_os, target_os_only,
   # Ensure our build/ directory is set up with the correct .gclient file.
   gclient_configure(solutions, target_os, target_os_only, git_cache_dir)
 
+  # Windows sometimes has trouble deleting files. This can make git commands
+  # that rely on locks fail.
+  break_repo_locks = True if sys.platform.startswith('win') else False
   # Let gclient do the DEPS syncing.
   # The branch-head refspec is a special case because its possible Chrome
   # src, which contains the branch-head refspecs, is DEPSed in.
-  gclient_output = gclient_sync(BRANCH_HEADS_REFSPEC in refs, shallow)
+  gclient_output = gclient_sync(BRANCH_HEADS_REFSPEC in refs, shallow,
+                                break_repo_locks)
 
   # Now that gclient_sync has finished, we should revert any .DEPS.git so that
   # presubmit doesn't complain about it being modified.

tests/bot_update_coverage_test.py

@@ -15,7 +15,6 @@ import unittest
 sys.path.insert(0, os.path.join(
     os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
     'recipe_modules', 'bot_update', 'resources'))
-sys.platform = 'linux2'  # For consistency, ya know?
 import bot_update
 
 DEFAULT_PARAMS = {
@@ -164,6 +163,7 @@ def fake_git(*args, **kwargs):
 
 class BotUpdateUnittests(unittest.TestCase):
   def setUp(self):
+    sys.platform = 'linux2'  # For consistency, ya know?
     self.filesystem = FakeFilesystem()
     self.call = MockedCall(self.filesystem)
     self.gclient = MockedGclientSync(self.filesystem)
@@ -195,6 +195,17 @@ class BotUpdateUnittests(unittest.TestCase):
     bot_update.ensure_checkout(**self.params)
     return self.call.records
 
+  def testBreakLocks(self):
+    sys.platform = 'win'
+    self.call.expect(('gclient.bat', 'sync')).returns(self.gclient)
+    bot_update.ensure_checkout(**self.params)
+    gclient_sync_cmd = None
+    for record in self.call.records:
+      args = record[0]
+      if args[0] == 'gclient.bat' and args[1] == 'sync':
+        gclient_sync_cmd = args
+    self.assertTrue('--break_repo_locks' in gclient_sync_cmd)
+
 
 if __name__ == '__main__':
   unittest.main()