Mypy fixes for `synapse.handlers.federation` (#8422)

For some reason, an apparently unrelated PR upset mypy about this module. Here are a number of little fixes.

1 files changed, 9 insertions, 4 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 5bcfb231b2..0073e7c996 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -155,8 +155,9 @@ class FederationHandler(BaseHandler):
             self._device_list_updater = hs.get_device_handler().device_list_updater
             self._maybe_store_room_on_invite = self.store.maybe_store_room_on_invite
 
-        # When joining a room we need to queue any events for that room up
-        self.room_queues = {}
+        # When joining a room we need to queue any events for that room up.
+        # For each room, a list of (pdu, origin) tuples.
+        self.room_queues = {}  # type: Dict[str, List[Tuple[EventBase, str]]]
         self._room_pdu_linearizer = Linearizer("fed_room_pdu")
 
         self.third_party_event_rules = hs.get_third_party_event_rules()
@@ -814,6 +815,9 @@ class FederationHandler(BaseHandler):
             dest, room_id, limit=limit, extremities=extremities
         )
 
+        if not events:
+            return []
+
         # ideally we'd sanity check the events here for excess prev_events etc,
         # but it's hard to reject events at this point without completely
         # breaking backfill in the same way that it is currently broken by
@@ -2164,10 +2168,10 @@ class FederationHandler(BaseHandler):
             # given state at the event. This should correctly handle cases
             # like bans, especially with state res v2.
 
-            state_sets = await self.state_store.get_state_groups(
+            state_sets_d = await self.state_store.get_state_groups(
                 event.room_id, extrem_ids
             )
-            state_sets = list(state_sets.values())
+            state_sets = list(state_sets_d.values())  # type: List[Iterable[EventBase]]
             state_sets.append(state)
             current_states = await self.state_handler.resolve_events(
                 room_version, state_sets, event
@@ -2958,6 +2962,7 @@ class FederationHandler(BaseHandler):
             )
             return result["max_stream_id"]
         else:
+            assert self.storage.persistence
             max_stream_token = await self.storage.persistence.persist_events(
                 event_and_contexts, backfilled=backfilled
             )