{"ast_node_type":"function","tokens":[{"end":66,"kind":"keyword","start":0,"text":"fn"}]}
    fn decode(decoder: &mut DecodeContext<'a, 'tcx>) -> SpanData {
impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for SpanData {
        let tag = SpanTag::decode(decoder);