{"ast_node_type":"function","tokens":[{"end":65,"kind":"keyword","start":0,"text":"fn"}]}
fn suggest_ref_mut(tcx: TyCtxt<'_>, span: Span) -> Option<Span> {
/// If possible, suggest replacing `ref` with `ref mut`.
    let pattern_str = tcx.sess.source_map().span_to_snippet(span).ok()?;