Macro define_compile_errors 

macro_rules! define_compile_errors {
    (
        $(
            $variant:ident {
                error = $error_msg:literal,
                label = $label_msg:literal,
                fields = { $( $field_name:ident : $field_ty:ty ),* $(,)? }
            }
        ),* $(,)?
    ) => { ... };
}