Macro cov::derive_serialize_with_interner

macro_rules! derive_serialize_with_interner {
    (
        $(#[$struct_attr:meta])*
        pub struct $struct_name:ident {
            $(
                $(#[$field_attr:meta])*
                pub $field_name:ident: $field_ty:ty,
            )+
        }
    ) => { ... };
    (direct: $($ty:ty),*) => { ... };
}