allow more kinds of empty structs

Author: joseph-gio

crates/bevy_macro_utils/src/lib.rs

@@ -158,7 +158,7 @@ pub fn derive_label(
             }
             // Structs must either be fieldless, or explicitly ignore the fields.
             let ignore_fields = input.attrs.iter().any(|a| is_ignore(a, attr_name));
-            if matches!(d.fields, syn::Fields::Unit) || ignore_fields {
+            if d.fields.is_empty() || ignore_fields {
                 let lit = ident.to_string();
                 let data = quote! { 0 };
                 let as_str = quote! { write!(f, #lit) };