Help with mixin into ArmorMaterials interface

[roman-emerald]

Description

I wanted to change vanilla armor stats
But when I try like so:

@Mixin(ArmorMaterials.class)
public interface MyMixin {
    @Shadow
    private static Map<EquipmentType, Integer> createDefenseMap(int bootsDefense, int leggingsDefense, int chestplateDefense, int helmetDefense, int bodyDefense) {
        return Maps.newEnumMap(Map.of(EquipmentType.BOOTS, bootsDefense, EquipmentType.LEGGINGS, leggingsDefense, EquipmentType.CHESTPLATE, chestplateDefense, EquipmentType.HELMET, helmetDefense, EquipmentType.BODY, bodyDefense));
    }

    @Shadow
    ArmorMaterial DIAMOND = new ArmorMaterial(
      5, createDefenseMap(1, 1, 1, 1, 1), 15, SoundEvents.ITEM_ARMOR_EQUIP_DIAMOND, 0.0F, 0.0F, ItemTags.REPAIRS_DIAMOND_ARMOR, EquipmentAssetKeys.DIAMOND
    );
}

Nothing changes... I'm new to java, can someone please tell me what is wrong?
I looked at changes it makes in .mixin.out and the value of DIAMOND is exactly the same as the vanilla
(I did register MyMixin in .mixins.json)

[Daomephsta]

@Shadow tells Mixin that a method or field is a "dummy" which exists only to make the Mixin compile, and shouldn't be merged into the target class.
A mixin consisting entirely of shadows is thus functionally the same as an empty mixin.

The ideal solution depends on exactly what changes you want to make to diamond armour, but for a crude "I just want it to work, then I'll make it good" solution, look into @Injecting into the <clinit> method (compiler generated method that contains all static field initialisers. You want to inject at TAIL so your reassignment of the field occurs after the initial assignment.

This does silently clobber any changes made by other mods though, so it shouldn't be used for anything other than learning purposes. The ideal way to do this depends on exactly what changes you want to make.

[roman-emerald]

Thanks for your answer, so injecting into would look like this?

@Inject(method = "<clinit>", at = @At("TAIL"))
    private static void quantumClinit(CallbackInfo ci) {
        DIAMOND = new ArmorMaterial(
                5, createDefenseMap(1, 1, 1, 1, 1), 15,
                SoundEvents.ITEM_ARMOR_EQUIP_LEATHER, 0.0F, 0.0F, ItemTags.REPAIRS_LEATHER_ARMOR, EquipmentAssetKeys.LEATHER
        );
    }

But when shadowing DIAMOND field like so:

@Final
@Mutable
@Shadow
ArmorMaterial DIAMOND;

Gives "Field 'DIAMOND' might not have been initialized"
and "Cannot assign a value to final variable 'DIAMOND'"

Maybe it's obvious but I'm stuck on this
How would I @Shadow the DIAMOND field to be assignable
Could you tell be please

[Daomephsta]

Cannot assign a value to final variable 'DIAMOND

Oh, I forgot that interface fields can only be final, so you can't write an interface mixin which assigns to an interface field because there's no way to make the code compile. Normally you'd have your shadow be @Final instead of final, but the compiler adds final, so that doesn't work for interface mixins.
That makes this significantly more complicated. You'll need to use @ModifyArgs to change the arguments passed to the ArmorMaterial constructor call, using @ModifyArgs.slice to restrict the scope of the @At so it only targets the initialiser of DIAMOND.

Field 'DIAMOND' might not have been initialized

Initialise it to null. Shadow methods and fields are just "dummies" to make the code compile.
The initialiser of a shadow field and the body of a shadow method are irrelevant because they're not merged into the target class.

[roman-emerald]

Yes, It worked! Didn't think that @ModifyArgs would work with constructor calls, but it does make sense.
Thanks for your help!