{"ast_node_type":"variable","tokens":[{"end":80,"kind":"keyword","start":0,"text":"let"}]}
    let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
    let sig = bound_sig.skip_binder();
    // `FnDef` and `FnPtr` only implement `AsyncFn*` when their