bot_update: improve UX when gclient is not configured.

recipe_modules/bot_update/api.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.
 
 
 """Recipe module to ensure a checkout is consistant on a bot."""
 
 from recipe_engine import recipe_api
 
 
@@ skipping 60 matching lines @@
         the 'rietveld' property.
       issue: The rietveld issue number to use. If omitted, will infer from
         the 'issue' property.
       patchset: The rietveld issue patchset to use. If omitted, will infer from
         the 'patchset' property.
     """
     refs = refs or []
     # We can re-use the gclient spec from the gclient module, since all the
     # data bot_update needs is already configured into the gclient spec.
     cfg = gclient_config or self.m.gclient.c
+    assert cfg is not None, (
+        'missing gclient_config or forgot api.gclient.set_config(...) before?')
 
     # Used by bot_update to determine if we want to run or not.
     master = self._mastername
     builder = self._buildername
     slave = self._slavename
 
     # Construct our bot_update command.  This basically be inclusive of
     # everything required for bot_update to know:
     root = patch_root
     if root is None:
@@ skipping 197 matching lines @@
 
         # bot_update actually just sets root to be the folder name of the
         # first solution.
         if step_result.json.output['did_run']:
           co_root = step_result.json.output['root']
           cwd = kwargs.get('cwd', self.m.path['slave_build'])
           if 'checkout' not in self.m.path:
             self.m.path['checkout'] = cwd.join(*co_root.split(self.m.path.sep))
 
     return step_result