Allow git_cl to be called when no default server is given

Review-Url: https://codereview.chromium.org/2109253002

git_cl.py

@@ -1595,6 +1595,7 @@ 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'
+    if not rietveld_server:
       settings.GetDefaultServerUrl()
 
     self._rietveld_server = rietveld_server
@@ -3448,17 +3449,23 @@ def CMDdescription(parser, args):
 
   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.')

tests/git_cl_test.py

@@ -1493,14 +1493,8 @@ class TestGitCl(TestCase):
   def test_description_rietveld(self):
     out = StringIO.StringIO()
     self.mock(git_cl.sys, 'stdout', out)
-    self.mock(git_cl.Changelist, 'GetDescription',
-              lambda *args: 'foobar')
+    self.mock(git_cl.Changelist, 'GetDescription', lambda *args: 'foobar')
 
-    self.calls = [
-        ((['git', 'config', 'rietveld.autoupdate'],), ''),
-        ((['git', 'config', 'rietveld.server'],), ''),
-        ((['git', 'config', 'rietveld.server'],), ''),
-    ]
     self.assertEqual(0, git_cl.main([
         'description', 'https://code.review.org/123123', '-d', '--rietveld']))
     self.assertEqual('foobar\n', out.getvalue())
@@ -1508,8 +1502,7 @@ class TestGitCl(TestCase):
   def test_description_gerrit(self):
     out = StringIO.StringIO()
     self.mock(git_cl.sys, 'stdout', out)
-    self.mock(git_cl.Changelist, 'GetDescription',
-              lambda *args: 'foobar')
+    self.mock(git_cl.Changelist, 'GetDescription', lambda *args: 'foobar')
 
     self.assertEqual(0, git_cl.main([
         'description', 'https://code.review.org/123123', '-d', '--gerrit']))