switch to setting default displayname in the storage layer

to avoid clobbering guest user displaynames on registration

synapse/rest/client/v2_alpha/register.py

@@ -20,7 +20,7 @@ import synapse
 import synapse.types
 from synapse.api.auth import get_access_token_from_request, has_access_token
 from synapse.api.constants import LoginType
-from synapse.types import RoomID, RoomAlias, get_localpart_from_id
+from synapse.types import RoomID, RoomAlias
 from synapse.api.errors import SynapseError, Codes, UnrecognizedRequestError
 from synapse.http.servlet import (
     RestServlet, parse_json_object_from_request, assert_params_in_request, parse_string
@@ -343,13 +343,6 @@ class RegisterRestServlet(RestServlet):
                 generate_token=False,
             )
 
-            # before we auto-join, set a default displayname to avoid ugly race
-            # between the client joining rooms and trying to set a displayname
-            localpart = get_localpart_from_id(registered_user_id)
-            yield self.store.set_profile_displayname(
-                localpart, localpart
-            )
-
             # auto-join the user to any rooms we're supposed to dump them into
             fake_requester = synapse.types.create_requester(registered_user_id)
             for r in self.hs.config.auto_join_rooms:

synapse/storage/registration.py

@@ -177,9 +177,11 @@ class RegistrationStore(background_updates.BackgroundUpdateStore):
             )
 
         if create_profile_with_localpart:
+            # set a default displayname serverside to avoid ugly race
+            # between auto-joins and clients trying to set displaynames
             txn.execute(
-                "INSERT INTO profiles(user_id) VALUES (?)",
-                (create_profile_with_localpart,)
+                "INSERT INTO profiles(user_id, displayname) VALUES (?,?)",
+                (create_profile_with_localpart, create_profile_with_localpart)
             )
 
         self._invalidate_cache_and_stream(