Macro http_types::format_err

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

Construct an ad-hoc error from a string.

This evaluates to an Error. It can take either just a string, or a format string with arguments. It also can take any custom type which implements Debug and Display.