{"ast_node_type":"variable","tokens":[{"end":88,"kind":"keyword","start":0,"text":"let"}]}
                            let variant_dest = lval.downcast_variant(fx, variant_index);
                        mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
                            (variant_index, variant_dest, active_field_index)