{"ast_node_type":"variable","tokens":[{"end":96,"kind":"keyword","start":0,"text":"let"}]}
        let ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(def_id)) = bound_var else {
    for bound_var in sig.bound_vars() {
            span_bug!(tcx.def_span(parent_def_id), "unexpected non-lifetime binder on fn sig");