{"ast_node_type":"variable","tokens":[{"end":31,"kind":"keyword","start":0,"text":"let"}]}
        let sub_tys = $sub_tys;
    (@pat(vec:$vec:expr, sub_tys:$sub_tys:expr, idx:$idx:expr, ctor:$ctor:expr) { $($fields:tt)* } $($rest:tt)*) => {{
        let index = $idx;