{"ast_node_type":"variable","tokens":[{"end":77,"kind":"keyword","start":0,"text":"let"}]}
    let sp = sp.macro_backtrace().last().map_or(sp, |trace| trace.call_site);
fn trace_macros_note(cx_expansions: &mut FxIndexMap<Span, Vec<String>>, sp: Span, message: String) {
    cx_expansions.entry(sp).or_default().push(message);