{"ast_node_type":"variable","tokens":[{"end":47,"kind":"keyword","start":0,"text":"let"}]}
        let source_map = tcx.sess.source_map();
    let fn_sig_span = maybe_fn_sig.map(|fn_sig| fn_sig.span).filter(|&fn_sig_span| {
        let file_idx = |span: Span| source_map.lookup_source_file_idx(span.lo());