{"ast_node_type":"other","tokens":[{"end":63,"kind":"keyword","start":0,"text":"(@fields(idx:$idx:expr,"}]}
    (@fields(idx:$idx:expr, $($args:tt)*) , $($rest:tt)*) => {{
    // Field without an explicit index; we use the current index which gets incremented above.
        pats!(@ctor($($args)*, idx:$idx) $($rest)*);