{"ast_node_type":"variable","tokens":[{"end":61,"kind":"keyword","start":0,"text":"let"}]}
            let prev = std::mem::replace(entry, hidden_type);
        if let Some(entry) = self.storage.opaque_types.get_mut(&key) {
            self.undo_log.push(UndoLog::OpaqueTypes(key, Some(prev)));