Better handling of odd PLs during room upgrades

Fixes handling of rooms where we have permission to send the tombstone, but not
other state. We need to (a) fail more gracefully when we can't send the PLs in
the old room, and (b) not set the PLs in the new room until we are done with
the other stuff.

changelog.d/4099.feature

+Support for replacing rooms with new ones

synapse/handlers/room.py

@@ -136,53 +136,91 @@ class RoomCreationHandler(BaseHandler):
                 requester, tombstone_event, tombstone_context,
             )
 
+            # and finally, shut down the PLs in the old room, and update them in the new
+            # room.
             old_room_state = yield tombstone_context.get_current_state_ids(self.store)
-            old_room_pl_event_id = old_room_state.get((EventTypes.PowerLevels, ""))
 
-            if old_room_pl_event_id is None:
-                logger.warning(
-                    "Not supported: upgrading a room with no PL event. Not setting PLs "
-                    "in old room.",
+            yield self._update_upgraded_room_pls(
+                requester, old_room_id, new_room_id, old_room_state,
+            )
+
+            defer.returnValue(new_room_id)
+
+    @defer.inlineCallbacks
+    def _update_upgraded_room_pls(
+            self, requester, old_room_id, new_room_id, old_room_state,
+    ):
+        """Send updated power levels in both rooms after an upgrade
+
+        Args:
+            requester (synapse.types.Requester): the user requesting the upgrade
+            old_room_id (unicode): the id of the room to be replaced
+            new_room_id (unicode): the id of the replacement room
+            old_room_state (dict[tuple[str, str], str]): the state map for the old room
+
+        Returns:
+            Deferred
+        """
+        old_room_pl_event_id = old_room_state.get((EventTypes.PowerLevels, ""))
+
+        if old_room_pl_event_id is None:
+            logger.warning(
+                "Not supported: upgrading a room with no PL event. Not setting PLs "
+                "in old room.",
+            )
+            return
+
+        old_room_pl_state = yield self.store.get_event(old_room_pl_event_id)
+
+        # we try to stop regular users from speaking by setting the PL required
+        # to send regular events and invites to 'Moderator' level. That's normally
+        # 50, but if the default PL in a room is 50 or more, then we set the
+        # required PL above that.
+
+        pl_content = dict(old_room_pl_state.content)
+        users_default = int(pl_content.get("users_default", 0))
+        restricted_level = max(users_default + 1, 50)
+
+        updated = False
+        for v in ("invite", "events_default"):
+            current = int(pl_content.get(v, 0))
+            if current < restricted_level:
+                logger.info(
+                    "Setting level for %s in %s to %i (was %i)",
+                    v, old_room_id, restricted_level, current,
                 )
+                pl_content[v] = restricted_level
+                updated = True
             else:
-                # we try to stop regular users from speaking by setting the PL required
-                # to send regular events and invites to 'Moderator' level. That's normally
-                # 50, but if the default PL in a room is 50 or more, then we set the
-                # required PL above that.
-
-                old_room_pl_state = yield self.store.get_event(old_room_pl_event_id)
-                pl_content = dict(old_room_pl_state.content)
-                users_default = int(pl_content.get("users_default", 0))
-                restricted_level = max(users_default + 1, 50)
-
-                updated = False
-                for v in ("invite", "events_default"):
-                    current = int(pl_content.get(v, 0))
-                    if current < restricted_level:
-                        logger.debug(
-                            "Setting level for %s in %s to %i (was %i)",
-                            v, old_room_id, restricted_level, current,
-                        )
-                        pl_content[v] = restricted_level
-                        updated = True
-                    else:
-                        logger.debug(
-                            "Not setting level for %s (already %i)",
-                            v, current,
-                        )
-
-                if updated:
-                    yield self.event_creation_handler.create_and_send_nonmember_event(
-                        requester, {
-                            "type": EventTypes.PowerLevels,
-                            "state_key": '',
-                            "room_id": old_room_id,
-                            "sender": user_id,
-                            "content": pl_content,
-                        }, ratelimit=False,
-                    )
-
-        defer.returnValue(new_room_id)
+                logger.info(
+                    "Not setting level for %s (already %i)",
+                    v, current,
+                )
+
+        if updated:
+            try:
+                yield self.event_creation_handler.create_and_send_nonmember_event(
+                    requester, {
+                        "type": EventTypes.PowerLevels,
+                        "state_key": '',
+                        "room_id": old_room_id,
+                        "sender": requester.user.to_string(),
+                        "content": pl_content,
+                    }, ratelimit=False,
+                )
+            except AuthError as e:
+                logger.warning("Unable to update PLs in old room: %s", e)
+
+        logger.info("Setting correct PLs in new room")
+        yield self.event_creation_handler.create_and_send_nonmember_event(
+            requester, {
+                "type": EventTypes.PowerLevels,
+                "state_key": '',
+                "room_id": new_room_id,
+                "sender": requester.user.to_string(),
+                "content": old_room_pl_state.content,
+            }, ratelimit=False,
+        )
 
     @defer.inlineCallbacks
     def clone_exiting_room(
@@ -223,7 +261,6 @@ class RoomCreationHandler(BaseHandler):
         initial_state = dict()
 
         types_to_copy = (
-            (EventTypes.PowerLevels, ""),
             (EventTypes.JoinRules, ""),
             (EventTypes.Name, ""),
             (EventTypes.Topic, ""),