Add some type hints to datastore (#12423)

* Add some type hints to datastore

* newsfile

* change `Collection` to `List`

* refactor return type of `select_users_txn`

* correct type hint in `stream.py`

* Remove `Optional` in `select_users_txn`

* remove not needed return type in `__init__`

* Revert change in `get_stream_id_for_event_txn`

* Remove import from `Literal`

synapse/storage/databases/main/stream.py

@@ -36,7 +36,17 @@ what sort order was used:
 """
 
 import logging
-from typing import TYPE_CHECKING, Any, Collection, Dict, List, Optional, Set, Tuple
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Collection,
+    Dict,
+    List,
+    Optional,
+    Set,
+    Tuple,
+    cast,
+)
 
 import attr
 from frozendict import frozendict
@@ -732,7 +742,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             A tuple of (stream ordering, topological ordering, event_id)
         """
 
-        def _f(txn):
+        def _f(txn: LoggingTransaction) -> Optional[Tuple[int, int, str]]:
             sql = (
                 "SELECT stream_ordering, topological_ordering, event_id"
                 " FROM events"
@@ -742,7 +752,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                 " LIMIT 1"
             )
             txn.execute(sql, (room_id, stream_ordering))
-            return txn.fetchone()
+            return cast(Optional[Tuple[int, int, str]], txn.fetchone())
 
         return await self.db_pool.runInteraction(
             "get_room_event_before_stream_ordering", _f
@@ -839,7 +849,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
     @staticmethod
     def _set_before_and_after(
         events: List[EventBase], rows: List[_EventDictReturn], topo_order: bool = True
-    ):
+    ) -> None:
         """Inserts ordering information to events' internal metadata from
         the DB rows.
 
@@ -985,7 +995,9 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             the `current_id`).
         """
 
-        def get_all_new_events_stream_txn(txn):
+        def get_all_new_events_stream_txn(
+            txn: LoggingTransaction,
+        ) -> Tuple[int, List[str]]:
             sql = (
                 "SELECT e.stream_ordering, e.event_id"
                 " FROM events AS e"
@@ -1331,7 +1343,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
     async def get_id_for_instance(self, instance_name: str) -> int:
         """Get a unique, immutable ID that corresponds to the given Synapse worker instance."""
 
-        def _get_id_for_instance_txn(txn):
+        def _get_id_for_instance_txn(txn: LoggingTransaction) -> int:
             instance_id = self.db_pool.simple_select_one_onecol_txn(
                 txn,
                 table="instance_map",