tools/git-sync-deps: speed up common case by skipping fetch

tools/git-sync-deps

 #!/usr/bin/python
 # Copyright 2014 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 """Parse a DEPS file and git checkout all of the dependencies.
 
 Args:
@@ skipping 115 matching lines @@
     # if the directory exists, but isn't a git repo, you will modify
     # the parent repostory, which isn't what you want.
     sys.stdout.write('%s\n  IS NOT TOP-LEVEL GIT DIRECTORY.\n' % directory)
     return
 
   # Check to see if this repo is disabled.  Quick return.
   if git_repository_sync_is_disabled(git, directory):
     sys.stdout.write('%s\n  SYNC IS DISABLED.\n' % directory)
     return
 
+  if 0 == subprocess.call(
+      [git, 'checkout', '--quiet', checkoutable], cwd=directory):
+    # if this succeeds, skip slow `git fetch`.
+    if verbose:
+      sys.stdout.write('%s\n  @ %s\n' % (directory, checkoutable))
+    return
+
   subprocess.check_call([git, 'fetch', '--quiet'], cwd=directory)
 
   subprocess.check_call(
     [git, 'checkout', '--quiet', checkoutable], cwd=directory)
 
   if verbose:
     sys.stdout.write('%s\n  @ %s\n' % (directory, checkoutable))  # Success.
 
 
 def parse_file_to_dict(path):
@@ skipping 23 matching lines @@
   os_specific_dependencies = deps_file.get('deps_os', [])
   for os_name in command_line_os_requests:
     # Add OS-specific dependencies
     if os_name in os_specific_dependencies:
       dependencies.update(os_specific_dependencies[os_name])
   list_of_arg_lists = []
   for directory in dependencies:
     if '@' in dependencies[directory]:
       repo, checkoutable = dependencies[directory].split('@', 1)
     else:
-      repo, checkoutable = dependencies[directory], 'origin/master'
+      raise Exception("please specify commit or tag")
 
     relative_directory = os.path.join(deps_file_directory, directory)
 
     list_of_arg_lists.append(
       (git, repo, checkoutable, relative_directory, verbose))
 
   multithread(git_checkout_to_directory, list_of_arg_lists)
 
   for directory in deps_file.get('recursedeps', []):
     recursive_path = os.path.join(deps_file_directory, directory, 'DEPS')
@@ skipping 20 matching lines @@
   if '--help' in argv or '-h' in argv:
     usage(deps_file_path)
     return 1
 
   git_sync_deps(deps_file_path, argv, verbose)
   return 0
 
 
 if __name__ == '__main__':
   exit(main(sys.argv[1:]))