Copy over non-federatable trait on room upgrade

changelog.d/4530.bugfix

@@ -0,0 +1 @@
+Copy over room federation ability on room upgrade.

synapse/handlers/room.py

@@ -263,6 +263,16 @@ def clone_existing_room(
             }
         }
 
+        # Check if old room was non-federatable
+
+        # Get old room's create event
+        old_room_create_event = yield self.store.get_create_event_for_room(old_room_id)
+
+        # Check if the create event specified a non-federatable room
+        if not old_room_create_event.content.get("m.federate", True):
+            # If so, mark the new room as non-federatable as well
+            creation_content["m.federate"] = False
+
         initial_state = dict()
 
         # Replicate relevant room events

synapse/storage/state.py

@@ -428,13 +428,9 @@ def get_room_version(self, room_id):
         """
         # for now we do this by looking at the create event. We may want to cache this
         # more intelligently in future.
-        state_ids = yield self.get_current_state_ids(room_id)
-        create_id = state_ids.get((EventTypes.Create, ""))
-
-        if not create_id:
-            raise NotFoundError("Unknown room %s" % (room_id))
 
-        create_event = yield self.get_event(create_id)
+        # Retrieve the room's create event
+        create_event = yield self.get_create_event_for_room(room_id)
         defer.returnValue(create_event.content.get("room_version", "1"))
 
     @defer.inlineCallbacks
@@ -447,19 +443,39 @@ def get_room_predecessor(self, room_id):
 
         Returns:
             Deferred[unicode|None]: predecessor room id
+
+        Raises:
+            NotFoundError if the room is unknown
+        """
+        # Retrieve the room's create event
+        create_event = yield self.get_create_event_for_room(room_id)
+
+        # Return predecessor if present
+        defer.returnValue(create_event.content.get("predecessor", None))
+
+    @defer.inlineCallbacks
+    def get_create_event_for_room(self, room_id):
+        """Get the create state event for a room.
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[EventBase]: The room creation event.
+
+        Raises:
+            NotFoundError if the room is unknown
         """
         state_ids = yield self.get_current_state_ids(room_id)
         create_id = state_ids.get((EventTypes.Create, ""))
 
         # If we can't find the create event, assume we've hit a dead end
         if not create_id:
-            defer.returnValue(None)
+            raise NotFoundError("Unknown room %s" % (room_id))
 
-        # Retrieve the room's create event
+        # Retrieve the room's create event and return
         create_event = yield self.get_event(create_id)
-
-        # Return predecessor if present
-        defer.returnValue(create_event.content.get("predecessor", None))
+        defer.returnValue(create_event)
 
     @cached(max_entries=100000, iterable=True)
     def get_current_state_ids(self, room_id):