Macro bail 

macro_rules! bail {
    ($msg:literal $(,)?) => { ... };
    ($err:expr $(,)?) => { ... };
    ($fmt:expr, $($arg:tt)*) => { ... };
}

Equivalent to return Err(Error::from_err(format_args!(...))) if a string literal, return Err(Error::from_err(expr)) if a single expression, or return Err(Error::from_err(format!(...))) otherwise.