{"ast_node_type":"variable","tokens":[{"end":90,"kind":"keyword","start":0,"text":"let"}]}
        let (sig, _) = tcx.hir_expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
    let mut impl_args = {
        sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))