{"ast_node_type":"variable","tokens":[{"end":39,"kind":"keyword","start":0,"text":"let"}]}
    let file = fs::File::open(&bc_path)
    let bc_path = in_incr_comp_dir_sess(tcx.sess, &filename);
        .unwrap_or_else(|e| panic!("failed to open bitcode file `{}`: {}", bc_path.display(), e));