Macro deprecated_function 

macro_rules! deprecated_function {
    (
        name = $name:expr,
        since = $since:expr,
        reason = $reason:expr
        $(, alternative = $alternative:expr)?
        $(, remove_in = $remove_in:expr)?
        $(, migration_notes = $notes:expr)?
        $(, level = $level:expr)?
    ) => { ... };
}

Macro to mark a function as deprecated with structured information