{"ast_node_type":"function","tokens":[{"end":100,"kind":"keyword","start":0,"text":"fn"}]}
    fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
    /// - `(TYPE,)`, a tuple with a single field of type TYPE.
        let mut trailing_plus = false;