{"ast_node_type":"function","tokens":[{"end":64,"kind":"keyword","start":0,"text":"//"}]}
    // sig = `fn (Pin<&mut proxy_ty>, &mut Context) -> Poll<()>`
    let env_ty = Ty::new_adt(tcx, pin_adt_ref, tcx.mk_args(&[proxy_ref.into()]));
    let sig = tcx.mk_fn_sig(