Macro log::warn

macro_rules! warn {
    (target: $target:expr, $($arg:tt)*) => { ... };
    ($($arg:tt)*) => { ... };
}

Logs a message at the warn level.

Logging at this level is disabled if any of the following features are present: max_level_off or max_level_error.

When building in release mode (i.e., without the debug_assertions option), logging at this level is also disabled if any of the following features are present: release_max_level_off or max_level_error.