{"ast_node_type":"other","tokens":[{"end":80,"kind":"keyword","start":0,"text":"(@fields(idx:$_idx:expr,"}]}
    (@fields(idx:$_idx:expr, $($args:tt)*) , .$idx:literal : $($rest:tt)*) => {{
    // `.i: pat` sets the current index to `i`.
        pats!(@ctor($($args)*, idx:$idx) $($rest)*);