{"ast_node_type":"variable","tokens":[{"end":100,"kind":"keyword","start":0,"text":"let"}]}
        let msg = format!("{} are not allowed in {}s", self.0.to_plural_string(), ccx.const_kind());
    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
        if let Status::Unstable { gate, .. } = self.status_in_item(ccx) {