{"ast_node_type":"function","tokens":[{"end":46,"kind":"keyword","start":0,"text":"fn"}]}
    fn decode(d: &mut D) -> GenericArg<'tcx> {
impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArg<'tcx> {
        GenericArgKind::decode(d).pack()