{"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
    let input = format!("#[derive({})]", pprust::path_to_string(path));
    // like `#[derive(Clone, Copy, Debug)]`.
    update_macro_stats(ecx, MacroKind::Derive, fragment_kind, span, path, &input, fragment);