Merge branch 'develop' of github.com:matrix-org/synapse into erikj/sqlite_native_upsert

synapse/storage/engines/sqlite.py

@@ -15,7 +15,6 @@
 
 import struct
 import threading
-from sqlite3 import sqlite_version_info
 
 from synapse.storage.prepare_database import prepare_database
 
@@ -40,7 +39,7 @@ class Sqlite3Engine(object):
         # when its enabled.
         # FIXME: Figure out what is wrong so we can re-enable native upserts
 
-        # return sqlite_version_info >= (3, 24, 0)
+        # return self.module.sqlite_version_info >= (3, 24, 0)
         return False
 
     def check_database(self, txn):

synapse/storage/state.py

@@ -437,6 +437,30 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
         create_event = yield self.get_event(create_id)
         defer.returnValue(create_event.content.get("room_version", "1"))
 
+    @defer.inlineCallbacks
+    def get_room_predecessor(self, room_id):
+        """Get the predecessor room of an upgraded room if one exists.
+        Otherwise return None.
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[unicode|None]: predecessor room id
+        """
+        state_ids = yield self.get_current_state_ids(room_id)
+        create_id = state_ids.get((EventTypes.Create, ""))
+
+        # If we can't find the create event, assume we've hit a dead end
+        if not create_id:
+            defer.returnValue(None)
+
+        # Retrieve the room's create event
+        create_event = yield self.get_event(create_id)
+
+        # Return predecessor if present
+        defer.returnValue(create_event.content.get("predecessor", None))
+
     @cached(max_entries=100000, iterable=True)
     def get_current_state_ids(self, room_id):
         """Get the current state event ids for a room based on the