{"ast_node_type":"struct","tokens":[{"end":35,"kind":"keyword","start":0,"text":"struct"}]}
        struct ProhibitOpaqueTypes;
    fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
        impl<'tcx> ty::TypeVisitor<TyCtxt<'tcx>> for ProhibitOpaqueTypes {