Macro claims

macro_rules! claims {
    (
        $(#[$meta:meta])*
        $vis:vis struct $name:ident {
            $(
                $(#[$field_meta:meta])*
                $field:ident : $type:ty
            ),* $(,)?
        }
    ) => { ... };
    (@gen_impl role) => { ... };
    (@gen_impl roles) => { ... };
    (@gen_impl permissions) => { ... };
    (@gen_impl $field:ident) => { ... };
}