{"ast_node_type":"function","tokens":[{"end":74,"kind":"keyword","start":0,"text":"pub"}]}
    pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
    /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
        match arg.kind() {