fn map_fields(
ion: &TokenStream,
fields: &mut Fields,
attribute: Either<&DataAttribute, &VariantAttribute>,
) -> Result<(Vec<Ident>, Vec<TokenStream>, bool)>fn map_fields(
ion: &TokenStream,
fields: &mut Fields,
attribute: Either<&DataAttribute, &VariantAttribute>,
) -> Result<(Vec<Ident>, Vec<TokenStream>, bool)>