Allow git_cl to be called when no default server is given

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 and Gerrit."""
 
 from __future__ import print_function
@@ skipping 1577 matching lines @@
 
     Issue must have been already uploaded and known.
     """
     raise NotImplementedError()
 
 
 class _RietveldChangelistImpl(_ChangelistCodereviewBase):
   def __init__(self, changelist, auth_config=None, rietveld_server=None):
     super(_RietveldChangelistImpl, self).__init__(changelist)
     assert settings, 'must be initialized in _ChangelistCodereviewBase'
-    settings.GetDefaultServerUrl()
+    if not rietveld_server:
+      settings.GetDefaultServerUrl()
 
     self._rietveld_server = rietveld_server
     self._auth_config = auth_config
     self._props = None
     self._rpc_server = None
 
   def GetCodereviewServer(self):
     if not self._rietveld_server:
       # If we're on a branch then get the server potentially associated
       # with that branch.
@@ skipping 1863 matching lines @@
   parser.add_option('-n', '--new-description',
                     help='New description to set for this issue (- for stdin)')
 
   _add_codereview_select_options(parser)
   auth.add_auth_options(parser)
   options, args = parser.parse_args(args)
   _process_codereview_select_options(parser, options)
 
   target_issue = None
   if len(args) > 0:
-    issue_arg = ParseIssueNumberArgument(args[0])
-    if not issue_arg.valid:
+    target_issue = ParseIssueNumberArgument(args[0])
+    if not target_issue.valid:
       parser.print_help()
       return 1
-    target_issue = issue_arg.issue
 
   auth_config = auth.extract_auth_config_from_options(options)
 
-  cl = Changelist(
-      auth_config=auth_config, issue=target_issue,
-      codereview=options.forced_codereview)
+  kwargs = {
+      'auth_config': auth_config,
+      'codereview': options.forced_codereview,
+  }
+  if target_issue:
+    kwargs['issue'] = target_issue.issue
+    if options.forced_codereview == 'rietveld':
+      kwargs['rietveld_server'] = target_issue.hostname
+
+  cl = Changelist(**kwargs)
 
   if not cl.GetIssue():
     DieWithError('This branch has no associated changelist.')
   description = ChangeDescription(cl.GetDescription())
 
   if options.display:
     print(description.description)
     return 0
 
   if options.new_description:
@@ skipping 1575 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   setup_color.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)