Send the m.room.create stripped event with invites (support MSC1772).

changelog.d/9915.feature

@@ -1 +1 @@
-Support stable identifiers from [MSC1772](https://github.com/matrix-org/matrix-doc/pull/1772).
+Support [MSC1772](https://github.com/matrix-org/matrix-doc/pull/1772).

changelog.d/9966.feature

@@ -0,0 +1 @@
+Support [MSC1772](https://github.com/matrix-org/matrix-doc/pull/1772).

docs/sample_config.yaml

@@ -1515,6 +1515,7 @@ room_prejoin_state:
    # - m.room.avatar
    # - m.room.encryption
    # - m.room.name
+   # - m.room.create
    #
    # Uncomment the following to disable these defaults (so that only the event
    # types listed in 'additional_event_types' are shared). Defaults to 'false'.

synapse/config/api.py

@@ -88,10 +88,6 @@ def _get_prejoin_state_types(self, config: JsonDict) -> Iterable[str]:
         if not room_prejoin_state_config.get("disable_default_event_types"):
             yield from _DEFAULT_PREJOIN_STATE_TYPES
 
-            if self.spaces_enabled:
-                # MSC1772 suggests adding m.room.create to the prejoin state
-                yield EventTypes.Create
-
         yield from room_prejoin_state_config.get("additional_event_types", [])
 
 
@@ -109,6 +105,8 @@ def _get_prejoin_state_types(self, config: JsonDict) -> Iterable[str]:
     EventTypes.RoomAvatar,
     EventTypes.RoomEncryption,
     EventTypes.Name,
+    # Per MSC1772.
+    EventTypes.Create,
 ]