{"ast_node_type":"variable","tokens":[{"end":52,"kind":"keyword","start":0,"text":"let"}]}
        let const_ty = self.constant()?.const_.ty();
    pub fn const_fn_def(&self) -> Option<(DefId, GenericArgsRef<'tcx>)> {
        if let ty::FnDef(def_id, args) = *const_ty.kind() { Some((def_id, args)) } else { None }