{"ast_node_type":"variable","tokens":[{"end":69,"kind":"keyword","start":0,"text":"let"}]}
    let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
    let firstch = src.chars().next()?;