Macro inner_star_join_flatmap_body 

macro_rules! inner_star_join_flatmap_body {
    (
        $stream1:expr,
        [$($stream:expr),+ $(,)?],
        $join_func:ident,
        [$($val_ty:ty),+ $(,)?],
        [$($trace_idx:tt),+ $(,)?],
        $k_ty:ty,
        $ov_ty:ty
    ) => { ... };
}