{"ast_node_type":"variable","tokens":[{"end":75,"kind":"keyword","start":0,"text":"let"}]}
    let hidden_ty = tcx.type_of(def_id.to_def_id()).instantiate(tcx, args);
    // here rather than using ReErased.
    let hidden_ty = fold_regions(tcx, hidden_ty, |re, _dbi| match re.kind() {