{"ast_node_type":"variable","tokens":[{"end":52,"kind":"keyword","start":0,"text":"let"}]}
        let source_map = self.tcx.sess.source_map();
    fn encode_source_map(&mut self) -> LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>> {
        let all_source_files = source_map.files();