streams: Disable inline URL preview when rendering stream descriptions.

We want to use the baseline features of bugdown, but not fancy things
like inline URL previews, since the whole structure of stream
descriptions is to have a single-line thing supporting some
formatting.

The migration part of this change fixes a bug encountered by some
organizations upgrading from older versions of Zulip.

zerver/lib/actions.py

@@ -1751,7 +1751,7 @@ def create_stream_if_needed(realm: Realm,
     )
 
     if created:
-        stream.rendered_description = bugdown_convert(stream.description)
+        stream.rendered_description = bugdown_convert(stream.description, no_previews=True)
         stream.save(update_fields=["rendered_description"])
         Recipient.objects.create(type_id=stream.id, type=Recipient.STREAM)
         if stream.is_public():
@@ -3505,7 +3505,7 @@ def do_rename_stream(stream: Stream,
 
 def do_change_stream_description(stream: Stream, new_description: str) -> None:
     stream.description = new_description
-    stream.rendered_description = bugdown_convert(new_description)
+    stream.rendered_description = bugdown_convert(new_description, no_previews=True)
     stream.save(update_fields=['description', 'rendered_description'])
 
     event = dict(

zerver/lib/bulk_create.py

@@ -80,7 +80,7 @@ def bulk_create_streams(realm: Realm,
                     realm=realm,
                     name=name,
                     description=options["description"],
-                    rendered_description=bugdown_convert(options["description"]),
+                    rendered_description=bugdown_convert(options["description"], no_previews=True),
                     invite_only=options.get("invite_only", False),
                     is_announcement_only=options.get("is_announcement_only", False),
                     history_public_to_subscribers=options["history_public_to_subscribers"],

zerver/lib/import_realm.py

@@ -746,7 +746,8 @@ def do_import_realm(import_dir: Path, subdomain: str, processes: int=1) -> Realm
     for stream in data['zerver_stream']:
         if 'rendered_description' in stream:
             continue
-        stream["rendered_description"] = bugdown_convert(stream["description"])
+        stream["rendered_description"] = bugdown_convert(stream["description"],
+                                                         no_previews=True)
     bulk_import_model(data, Stream)
 
     realm.notifications_stream_id = notifications_stream_id

zerver/migrations/0206_stream_rendered_description.py

@@ -12,7 +12,8 @@ def render_all_stream_descriptions(apps: StateApps, schema_editor: DatabaseSchem
     Stream = apps.get_model('zerver', 'Stream')
     all_streams = Stream.objects.exclude(description='')
     for stream in all_streams:
-        stream.rendered_description = bugdown_convert(stream.description)
+        stream.rendered_description = bugdown_convert(stream.description,
+                                                      no_previews=True)
         stream.save(update_fields=["rendered_description"])
 
 

zerver/tests/test_subs.py

@@ -708,6 +708,16 @@ class StreamAdminTest(ZulipTestCase):
         stream = get_stream('stream_name1', realm)
         self.assertEqual(stream.description, 'a multi line description')
 
+        # Verify that we don't render inline URL previews in this code path.
+        with self.settings(INLINE_URL_EMBED_PREVIEW=True):
+            result = self.client_patch('/json/streams/%d' % (stream_id,),
+                                       {'description': ujson.dumps('See https://zulipchat.com/team')})
+        self.assert_json_success(result)
+        stream = get_stream('stream_name1', realm)
+        self.assertEqual(stream.rendered_description,
+                         '<p>See <a href="https://zulipchat.com/team" target="_blank" '
+                         'title="https://zulipchat.com/team">https://zulipchat.com/team</a></p>')
+
     def test_change_stream_description_requires_realm_admin(self) -> None:
         user_profile = self.example_user('hamlet')
         email = user_profile.email