show heroes if a room has a 'deleted' name/canonical_alias (#3851)

changelog.d/3851.bugfix

@@ -0,0 +1 @@
+Show heroes if room name/canonical alias has been deleted

synapse/handlers/sync.py

@@ -562,8 +562,21 @@ class SyncHandler(object):
             details.get(Membership.INVITE, empty_ms).count
         )
 
-        if name_id or canonical_alias_id:
+        # if the room has a name or canonical_alias set, we can skip
-            defer.returnValue(summary)
+        # calculating heroes.  we assume that if the event has contents, it'll
+        # be a valid name or canonical_alias - i.e. we're checking that they
+        # haven't been "deleted" by blatting {} over the top.
+        if name_id:
+            name = yield self.store.get_event(name_id, allow_none=False)
+            if name and name.content:
+                defer.returnValue(summary)
+
+        if canonical_alias_id:
+            canonical_alias = yield self.store.get_event(
+                canonical_alias_id, allow_none=False,
+            )
+            if canonical_alias and canonical_alias.content:
+                defer.returnValue(summary)
 
         joined_user_ids = [
             r[0] for r in details.get(Membership.JOIN, empty_ms).members