{"ast_node_type":"function","tokens":[{"end":99,"kind":"keyword","start":0,"text":"fn"}]}
    fn insert_spec(&mut self, id: LintId, LevelAndSource { level, lint_id, src }: LevelAndSource) {
    /// diagnostic with no change to `specs`.
        let LevelAndSource { level: old_level, src: old_src, .. } =