Macro span

macro_rules! span {
    (target: $target:expr, $lvl:expr, $name:expr, $($fields:tt)*) => { ... };
    (target: $target:expr, $lvl:expr, $name:expr) => { ... };
    ($lvl:expr, $name:expr, $($fields:tt)*) => { ... };
    ($lvl:expr, $name:expr) => { ... };
}

Available on crate feature tracing only.

A macro to create a span.