1 files changed, 10 insertions, 6 deletions
diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py
index dbaeef91dd..d89f6ed128 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -18,7 +18,7 @@
 import itertools
 import logging
 from collections import deque, namedtuple
-from typing import Iterable, List, Optional, Set, Tuple
+from typing import Dict, Iterable, List, Optional, Set, Tuple
 
 from prometheus_client import Counter, Histogram
 
@@ -31,7 +31,7 @@ from synapse.logging.context import PreserveLoggingContext, make_deferred_yielda
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.databases import Databases
 from synapse.storage.databases.main.events import DeltaState
-from synapse.types import StateMap
+from synapse.types import Collection, StateMap
 from synapse.util.async_helpers import ObservableDeferred
 from synapse.util.metrics import Measure
 
@@ -185,6 +185,8 @@ class EventsPersistenceStorage:
         # store for now.
         self.main_store = stores.main
         self.state_store = stores.state
+
+        assert stores.persist_events
         self.persist_events_store = stores.persist_events
 
         self._clock = hs.get_clock()
@@ -208,7 +210,7 @@ class EventsPersistenceStorage:
         Returns:
             the stream ordering of the latest persisted event
         """
-        partitioned = {}
+        partitioned = {}  # type: Dict[str, List[Tuple[EventBase, EventContext]]]
         for event, ctx in events_and_contexts:
             partitioned.setdefault(event.room_id, []).append((event, ctx))
 
@@ -305,7 +307,9 @@ class EventsPersistenceStorage:
                     # Work out the new "current state" for each room.
                     # We do this by working out what the new extremities are and then
                     # calculating the state from that.
-                    events_by_room = {}
+                    events_by_room = (
+                        {}
+                    )  # type: Dict[str, List[Tuple[EventBase, EventContext]]]
                     for event, context in chunk:
                         events_by_room.setdefault(event.room_id, []).append(
                             (event, context)
@@ -436,7 +440,7 @@ class EventsPersistenceStorage:
         self,
         room_id: str,
         event_contexts: List[Tuple[EventBase, EventContext]],
-        latest_event_ids: List[str],
+        latest_event_ids: Collection[str],
     ):
         """Calculates the new forward extremities for a room given events to
         persist.
@@ -470,7 +474,7 @@ class EventsPersistenceStorage:
         # Remove any events which are prev_events of any existing events.
         existing_prevs = await self.persist_events_store._get_events_which_are_prevs(
             result
-        )
+        )  # type: Collection[str]
         result.difference_update(existing_prevs)
 
         # Finally handle the case where the new events have soft-failed prev