Add an error message when explicitly specifying bots without specifying the master

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 2166 matching lines @@
   if args:
     parser.error('Unknown arguments: %s' % args)
 
   cl = Changelist()
   if not cl.GetIssue():
     parser.error('Need to upload first')
 
   if not options.name:
     options.name = cl.GetBranch()
 
+  if options.bot and not options.master:
+    parser.error('For manually specified bots please also specify the '
+                 'tryserver master, e.g. "-m tryserver.chromium".')
+
   def GetMasterMap():
     # Process --bot and --testfilter.
     if not options.bot:
       change = cl.GetChange(cl.GetCommonAncestorWithUpstream(), None)
 
       # Get try masters from PRESUBMIT.py files.
       masters = presubmit_support.DoGetTryMasters(
           change,
           change.LocalPaths(),
           settings.GetRoot(),
@@ skipping 334 matching lines @@
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   sys.exit(main(sys.argv[1:]))