Stop depending on room_id to be returned for children state in the …

…hierarchy response. (#12991)

The `room_id` field was removed from MSC2946 before
it was accepted. It was initially kept for backwards compatibility
and should be removed now that the stable form of the API
is used.

This change only stops Synapse from validating that it is returned,
a future PR will remove returning it as part of the response.

changelog.d/12991.bugfix

@@ -0,0 +1,2 @@
+Fix a bug where non-standard information was required when requesting the `/hierarchy` API over federation. Introduced 
+in Synapse v1.41.0.

synapse/federation/federation_client.py

@@ -1642,10 +1642,6 @@ def _validate_hierarchy_event(d: JsonDict) -> None:
     if not isinstance(event_type, str):
         raise ValueError("Invalid event: 'event_type' must be a str")
 
-    room_id = d.get("room_id")
-    if not isinstance(room_id, str):
-        raise ValueError("Invalid event: 'room_id' must be a str")
-
     state_key = d.get("state_key")
     if not isinstance(state_key, str):
         raise ValueError("Invalid event: 'state_key' must be a str")

tests/handlers/test_room_summary.py

@@ -178,7 +178,7 @@ def _assert_hierarchy(
             result_room_ids.append(result_room["room_id"])
             result_children_ids.append(
                 [
-                    (cs["room_id"], cs["state_key"])
+                    (result_room["room_id"], cs["state_key"])
                     for cs in result_room["children_state"]
                 ]
             )