Fabric custom item model loading

BCSiliconModels.java

// A cut down version. This isn't compilabale as-is!

public class BCSiliconModels {
  public static final ModelIdentifier CHIPSET_PART_A = new ModelIdentifier("buildcraftsilicon:redstone_chipset_a#inventory");
  public static final ModelIdentifier CHIPSET_PART_B = new ModelIdentifier("buildcraftsilicon:redstone_chipset_b#inventory");
  
  /** Called by the ClientModInitialiser */
  public static void load() {
    ModelLoadingRegistry.INSTANCE.registerAppender((manager, out) -> {
      out.accept(CHIPSET_PART_A);
      out.accept(CHIPSET_PART_B);
    });
    ModelLoadingRegistry.INSTANCE.registerVariantProvider(res -> (id, ctx) -> {
      // The identifer for the item we want to replace
      if ("buildcraft_silicon:redstone_chipset#inventory".equals(id.toString())) {
        return new PreBakedModel(new BakedModel(){
          // Override all the normal methods to return either empty lists or something else
          // The point is it's not imporatant, as they won't be used
          
          final ModelItemPropertyOverrideList overrideList
            = new ModelItemPropertyOverrideList(null, null, null, Collections.emptyList()) {
            
              @Override
              public BakedModel apply(BakedModel original, ItemStack stack, World world, LivingEntity entity) {
                if (shouldUseVariantA(stack)) {
                  return MinecraftClient.getInstance().getBakedModelManager().getModel(CHIPSET_PART_A); 
                } else {
                  return MinecraftClient.getInstance().getBakedModelManager().getModel(CHIPSET_PART_B); 
                }
              }
          };
          
          @Override
          public ModelItemPropertyOverrideList getItemPropertyOverrides() {
            return overrideList;
          }
        });
      }
      return null;
    });
  }
}

PreBakedModel.java

package buildcraft.lib.client.model;

import java.util.Collection;
import java.util.Collections;
import java.util.Set;
import java.util.function.Function;

import net.minecraft.client.render.model.BakedModel;
import net.minecraft.client.render.model.ModelBakeSettings;
import net.minecraft.client.render.model.ModelLoader;
import net.minecraft.client.render.model.UnbakedModel;
import net.minecraft.client.texture.Sprite;
import net.minecraft.util.Identifier;

public final class PreBakedModel implements UnbakedModel {

    private final BakedModel baked;

    public PreBakedModel(BakedModel baked) {
        this.baked = baked;
    }

    @Override
    public Collection<Identifier> getModelDependencies() {
        return Collections.emptyList();
    }

    @Override
    public Collection<Identifier> getTextureDependencies(Function<Identifier, UnbakedModel> var1, Set<String> var2) {
        return Collections.emptyList();
    }

    @Override
    public BakedModel bake(ModelLoader var1, Function<Identifier, Sprite> var2, ModelBakeSettings var3) {
        return baked;
    }
}