{"ast_node_type":"variable","tokens":[{"end":85,"kind":"keyword","start":0,"text":"let"}]}
                    let Some(mut variant) = variants.nth(variant_index.into()) else {
                    let mut variants = args.as_coroutine().state_tys(def_id, tcx);
                        bug!("variant {variant_index:?} of coroutine out of range: {self_ty:?}");