Transfer power level state events on room upgrade

changelog.d/6237.bugfix

@@ -0,0 +1 @@
+Transfer non-standard power levels on room upgrade.

synapse/handlers/room.py

@@ -211,8 +211,8 @@ def _update_upgraded_room_pls(
 
         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_id (str): the id of the room to be replaced
+            new_room_id (str): the id of the replacement room
             old_room_state (dict[tuple[str, str], str]): the state map for the old room
 
         Returns:
@@ -333,6 +333,7 @@ def clone_existing_room(
             (EventTypes.Encryption, ""),
             (EventTypes.ServerACL, ""),
             (EventTypes.RelatedGroups, ""),
+            (EventTypes.PowerLevels, ""),  # Removed before sending in the new room
         )
 
         old_room_state_ids = yield self.store.get_filtered_current_state_ids(
@@ -346,6 +347,31 @@ def clone_existing_room(
             if old_event:
                 initial_state[k] = old_event.content
 
+        # Copy over user power levels now as this will not be possible with >100PL users once
+        # the room has been created
+        old_user_power_levels = initial_state[(EventTypes.PowerLevels, "")].get("users")
+        new_user_power_levels = None
+        if old_user_power_levels:
+            user_level_dict = {}
+
+            # Track the maximum power level in the old room, and temporarily make the
+            # upgrading user this power level so that they can replicate all state events over
+            # They will be returned to their original power level later
+            max_power_level = 100
+            for user, power_level in old_user_power_levels.items():
+                power_level = int(power_level)
+                user_level_dict[user] = power_level
+                max_power_level = max(max_power_level, power_level)
+
+            # Upgrade the requester to the max known room power level so that
+            # they're allowed to send any state event in the new room
+            user_level_dict[requester.user.to_string()] = max_power_level
+            new_user_power_levels = {"users": user_level_dict}
+
+        # Prevent the rest of the power level events from being transferred now. They will
+        # be transferred later after the room state has been established
+        del initial_state[(EventTypes.PowerLevels, "")]
+
         yield self._send_events_for_new_room(
             requester,
             new_room_id,
@@ -355,6 +381,7 @@ def clone_existing_room(
             invite_list=[],
             initial_state=initial_state,
             creation_content=creation_content,
+            power_level_content_override=new_user_power_levels,
         )
 
         # Transfer membership events