Docserver: Persist stat cache for versioned file systems

chrome/common/extensions/docs/server2/gitiles_file_system.py

 # Copyright 2014 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.
 
 
 from base64 import b64decode
 from itertools import izip
 import json
 import logging
 import posixpath
@@ skipping 215 matching lines @@
         return stat_info
       if filename not in stat_info.child_versions:
         raise FileNotFoundError(
             '%s from %s was not in child versions for Stat' % (filename, path))
       return StatInfo(stat_info.child_versions[filename])
 
     fetch_future = self._FetchAsync(ToDirectory(dir_) + _JSON_FORMAT)
     return self._ResolveFetchContent(path, fetch_future).Then(stat)
 
   def GetIdentity(self):
-    # NOTE: Do not use commit information to create the string identity.
-    # Doing so will mess up caching.
-    if self._commit is None and self._branch != 'master':
-      str_id = '%s/%s/%s/%s' % (
-          GITILES_BASE, GITILES_SRC_ROOT, GITILES_BRANCHES_PATH, self._branch)
+    if self._branch == 'master':
+      # A master FS always carries the same identity even if pinned to a commit.
+      str_id = 'master'
+    elif self._commit is not None:
+      str_id = self._commit
     else:
-      str_id = '%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT)
-    return '@'.join((self.__class__.__name__, StringIdentity(str_id)))
+      str_id = '%s/%s' % (GITILES_BRANCHES_PATH, self._branch)
+    return '@'.join(self.__class__.__name__, StringIdentity(
+        '%s/%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT, str_id)))
+
+  def GetVersion(self):
+    return self._commit