Macro panic_2015 

#[doc(hidden)]
pub macro panic_2015 {
    () => { ... },
    ($msg:literal $(,)?) => { ... },
    ($msg:expr $(,)?) => { ... },
    ("{}", $arg:expr $(,)?) => { ... },
    ($fmt:expr, $($arg:tt)+) => { ... },
}

🔬This is a nightly-only experimental API. (edition_panic)