{"ast_node_type":"variable","tokens":[{"end":80,"kind":"keyword","start":0,"text":"let"}]}
    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, span));
    // ret_ty = `Poll<()>`
    let ret_ty = Ty::new_adt(tcx, poll_adt_ref, tcx.mk_args(&[tcx.types.unit.into()]));