Adding the posibility to add custom conditions for custom variants

[AngelDGr]

Describe the Addition

Currently, it seems that the only available conditions for assigning (or not assigning) new variants to the book are "mod_loaded", "not", "and", and "or".

While this is useful, some of my variants depend on a Forge config, which makes the default system insufficient for my use case.

I managed to add a custom condition using a simple mixin like this:

@Mixin(VariantConditionEvaluator.class)
public class VariantConditionEvaluatorMixin {

    @Inject(method = "evaluate", at = @At("HEAD"), cancellable = true)
    private static void primal$addConfigCondition(JsonObject condition, CallbackInfoReturnable<Boolean> cir) {

        if(condition.get("type").getAsString().equals("is_primal_rabbit_enabled")){
            cir.setReturnValue(Primal_Main.ConfigCache.rabbitModelChange);
        }
    }
}

And my JSON looks like this:

{
  "replace": false,
  "entries": [
    {
      "id": "minecraft:rabbit",
      "conditions": [
        {
          "type": "is_primal_rabbit_enabled"
        }
      ],
      "variants": [
        {
          "id": "gray",
          "nbt": "{RabbitType:7}"
        },
        {
          "id": "sand",
          "nbt": "{RabbitType:8}"
        }
      ]
    }
  ]
}

}

This works well, but it would be great to have a built-in way to define custom conditions.

In any case, I really like how this mod is evolving, and I’m excited about its future!

Screenshots and Videos

No response

Additional Context

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