Macro dim_utils::balanced_or_tree

macro_rules! balanced_or_tree {
    ($x:expr $(,)?) => { ... };
    ($($x:expr),+ $(,)?) => { ... };
    (@internal $($left:expr),*; $head:expr, $($tail:expr),+; $a:expr $(,$b:expr)?) => { ... };
    (@internal $($left:expr),*; $head:expr, $($tail:expr),+; $a:expr, $b:expr, $($more:expr),+) => { ... };
}

Source: https://github.com/seanmonstar/warp/issues/619 Takes a list of handler expressions and ors them together in a balanced tree. That is, instead of a.or(b).or(c).or(d), it produces (a.or(b)).or(c.or(d)), thus nesting the types less deeply, which provides improvements in compile time.

It also applies ::warp::Filter::boxed to each handler expression when in debug_assertions mode, improving compile time further.