{"ast_node_type":"variable","tokens":[{"end":46,"kind":"keyword","start":0,"text":"if"}]}
        if let Some((_, _)) = self.stability {
    fn check_duplicate<S: Stage>(&self, cx: &AcceptContext<'_, '_, S>) -> bool {
            cx.emit_err(session_diagnostics::MultipleStabilityLevels { span: cx.attr_span });