Don't needlessly compute prev_state

synapse/handlers/_base.py

@@ -78,7 +78,9 @@ class BaseHandler(object):
         context = yield state_handler.compute_event_context(builder)
 
         if builder.is_state():
-            builder.prev_state = context.prev_state_events
+            builder.prev_state = yield self.store.add_event_hashes(
+                context.prev_state_events
+            )
 
         yield self.auth.add_auth_events(builder, context)
 

synapse/state.py

@@ -155,10 +155,6 @@ class StateHandler(object):
         context.current_state = curr_state
         context.state_group = group if not event.is_state() else None
 
-        prev_state = yield self.store.add_event_hashes(
-            prev_state
-        )
-
         if event.is_state():
             key = (event.type, event.state_key)
             if key in context.current_state:

tests/handlers/test_room.py

@@ -42,6 +42,7 @@ class RoomMemberHandlerTestCase(unittest.TestCase):
                 "get_room",
                 "store_room",
                 "get_latest_events_in_room",
+                "add_event_hashes",
             ]),
             resource_for_federation=NonCallableMock(),
             http_client=NonCallableMock(spec_set=[]),
@@ -88,6 +89,7 @@ class RoomMemberHandlerTestCase(unittest.TestCase):
         self.ratelimiter.send_message.return_value = (True, 0)
 
         self.datastore.persist_event.return_value = (1,1)
+        self.datastore.add_event_hashes.return_value = []
 
     @defer.inlineCallbacks
     def test_invite(self):