Macro http_error_fmt 

macro_rules! http_error_fmt {
    ($(#[$meta:meta])* $vis:vis $name:ident, $status:expr, |$ty_self:pat, $fmt:ident| $body:expr $(,)?) => { ... };
}

Defines a zero-sized type that implements [HttpError] with a custom formatter.

This macro is intended for library users who want lightweight marker error types that only carry a status code and a display representation.