labhub: Allow missing username and msg link

Some backends do not provide usernames or msg links.

Zulip and Slack both using msg.extra['url'], and a
patch is pending for the gitter backend to follow suite.
errbotio/err-backend-gitter#32

Fixes coala#392
Related to coala#255

plugins/labhub.py

@@ -154,11 +154,20 @@ def create_issue_cmd(self, msg, match):
         repo_name = match.group(1)
         iss_title = match.group(2)
         iss_description = match.group(3) if match.group(3) is not None else ''
-        extra_msg = '\nOpened by @{username} at [{backend}]({msg_link})'.format(
-            username=msg.frm.nick,
-            backend=self.bot_config.BACKEND,
-            msg_link=message_link(self, msg)
-        )
+
+        extra_parts = []
+        if msg.frm.nick:
+            extra_parts.append('by @{}'.format(msg.frm.nick))
+        msg_link = message_link(self, msg)
+        if msg_link:
+            extra_parts.append(' at [{backend}]({msg_link})'.format(
+                backend=self.bot_config.BACKEND,
+                msg_link=message_link(self, msg)
+            )
+        else:
+            extra_parts.append(' on {}'.format(self.bot_config.BACKEND))
+
+        extra_msg = '\nOpened {}'.format(' '.join(extra_parts))
 
         if repo_name in self.REPOS:
             repo = self.REPOS[repo_name]

tests/labhub_test.py

@@ -95,14 +95,14 @@ def test_create_issue_cmd(self):
                               'Here you go')
 
         labhub.REPOS['repository'].create_issue.assert_called_once_with(
-            'this is the title', 'bo\ndy\nOpened by @None at [text]()'
+            'this is the title', 'bo\ndy\nOpened at [text]()'
         )
 
         testbot.assertCommand('!new issue repository.github.io another title\nand body',
                               'Here you go')
 
         labhub.REPOS['repository.github.io'].create_issue.assert_called_with(
-            'another title', 'and body\nOpened by @None at [text]()'
+            'another title', 'and body\nOpened at [text]()'
         )
 
         testbot.assertCommand('!new issue coala title', 'repository that does not exist')

utils/backends.py

@@ -12,11 +12,7 @@ def message_link(bot, msg):
     if backend == 'gitter':
         return 'https://gitter.im/{uri}?at={idd}'.format(uri=msg.frm.room.uri,
                                                          idd=msg.extras['id'])
-    elif backend == 'slack':
+    elif 'url' in msg.extras:
         return msg.extras['url']
-    elif backend == 'telegram':
-        return ''
-    elif backend == 'text':
-        return ''
     else:
-        raise NotImplementedError
+        return None