{"ast_node_type":"variable","tokens":[{"end":36,"kind":"keyword","start":0,"text":"let"}]}
    let span = tcx.def_span(def_id);
    assert_matches!(self_ty.kind(), ty::FnPtr(..), "expected fn ptr, found {self_ty}");
    let Some(sig) = tcx.fn_sig(def_id).instantiate(tcx, &[self_ty.into()]).no_bound_vars() else {