{"ast_node_type":"variable","tokens":[{"end":78,"kind":"keyword","start":0,"text":"let"}]}
    let Some(first_span) = (try { fn_cov_info.mappings.first()?.span }) else {
    let source_map = tcx.sess.source_map();
        debug_assert!(false, "function has no mappings: {covfun:?}");