{"ast_node_type":"variable","tokens":[{"end":38,"kind":"keyword","start":0,"text":"let"}]}
    let sig = bound_sig.skip_binder();
) -> Result<(ty::Binder<I, AsyncCallableRelevantTypes<I>>, Vec<I::Predicate>), NoSolution> {
    let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);