macro_rules! back_alley {
    ( $( $fmt:literal $( , $arg:expr )* )? ) => {
        #[cfg(debug_assertions)]
        {
            unsafe fn __back_alley_internal() {}
            __back_alley_internal();
            unreachable!( $( $fmt $( , $arg )* )? );
        }
        #[cfg(not_debug_assertions)]
        core::hint::unreachable_unchecked();
    };
}

fn main() {
    loop { break; }
    unsafe { back_alley!("uh oh, {}", "sisters"); }
}