Add final type hint to synapse.server. (#15035)

synapse/storage/_base.py

@@ -37,6 +37,8 @@ class SQLBaseStore(metaclass=ABCMeta):
     per data store (and not one per physical database).
     """
 
+    db_pool: DatabasePool
+
     def __init__(
         self,
         database: DatabasePool,

synapse/storage/database.py

@@ -499,6 +499,7 @@ class DatabasePool:
     """
 
     _TXN_ID = 0
+    engine: BaseDatabaseEngine
 
     def __init__(
         self,

synapse/storage/databases/main/events.py

@@ -306,7 +306,7 @@ class PersistEventsStore:
 
         # The set of event_ids to return. This includes all soft-failed events
         # and their prev events.
-        existing_prevs = set()
+        existing_prevs: Set[str] = set()
 
         def _get_prevs_before_rejected_txn(
             txn: LoggingTransaction, batch: Collection[str]