{"ast_node_type":"variable","tokens":[{"end":78,"kind":"keyword","start":0,"text":"let"}]}
    let pin_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, span));
    // env_ty = `Pin<&mut proxy_ty>`
    let env_ty = Ty::new_adt(tcx, pin_adt_ref, tcx.mk_args(&[proxy_ref.into()]));