{"ast_node_type":"function","tokens":[{"end":72,"kind":"keyword","start":0,"text":"fn"}]}
    fn map_trait_to_async_trait(&self, def_id: DefId) -> Option<DefId> {
    /// lowering of `async Fn()` bounds to desugar to another trait like `LendingFn`.
        let lang_items = self.tcx.lang_items();