{"ast_node_type":"other","tokens":[{"end":94,"kind":"keyword","start":0,"text":"//"}]}
        // If the rhs contains an invocation like `compile_error!`, don't report it as unused.
    pub fn get_unused_rule(&self, rule_i: usize) -> Option<(&Ident, Span)> {
        let rule = &self.rules[rule_i];