Experimental DynamicRegistriesLoaded hook for minecraft forge

BiomeAccessor.java

package commoble.dynamicregistrycheeser.mixin;

import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.gen.Accessor;

import net.minecraft.world.biome.Biome;
import net.minecraft.world.biome.BiomeGenerationSettings;

@Mixin(Biome.class)
public interface BiomeAccessor
{
	// TODO replace with AT
	@Accessor
	void setGenerationSettings(BiomeGenerationSettings generationSettings);
}

DynamicRegistryCheeser.java

package commoble.dynamicregistrycheeser;

import javax.annotation.Nonnull;

import commoble.dynamicregistrycheeser.mixin.BiomeAccessor;
import net.minecraft.util.RegistryKey;
import net.minecraft.util.ResourceLocation;
import net.minecraft.util.registry.DynamicRegistries;
import net.minecraft.util.registry.Registry;
import net.minecraft.world.gen.GenerationStage.Decoration;
import net.minecraft.world.gen.feature.ConfiguredFeature;
import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.common.world.BiomeGenerationSettingsBuilder;
import net.minecraftforge.eventbus.api.Event;
import net.minecraftforge.eventbus.api.IEventBus;
import net.minecraftforge.fml.common.Mod;

@Mod(DynamicRegistryCheeser.MODID)
public class DynamicRegistryCheeser
{
	public static final String MODID = "dynamicregistrycheeser";
	
	public static final RegistryKey<ConfiguredFeature<?,?>> TEST_FEATURE = RegistryKey.create(Registry.CONFIGURED_FEATURE_REGISTRY,
		new ResourceLocation("dynamicregistrycheeser:test_pile"));
	
	public DynamicRegistryCheeser()
	{
		IEventBus forgeBus = MinecraftForge.EVENT_BUS;
		
		forgeBus.addListener(this::onDynamicRegistriesLoaded);
	}
	
	// event is fired at the end of WorldSettingsImport::create (the overload that takes a resource manager, not an IResourceAccess)
	// the IResourceAccess one is a bit more generic and is also used when loading up the builtin vanilla stuff before datapacks are added.
	// the resource manager one is called to add datapack stuff, firing the event at the end of the method results in the event
	// firing after datapacks are loaded into the dynamic registries.
	void onDynamicRegistriesLoaded(DynamicRegistriesLoadedEvent event)
	{
		DynamicRegistries.Impl registries = event.getRegistries();
		registries.registry(Registry.BIOME_REGISTRY)
			.ifPresent(biomeRegistry -> registries.registry(Registry.CONFIGURED_FEATURE_REGISTRY)
				.ifPresent(featureRegistry ->
				{
					// let's add a datapack feature to each biome
					ConfiguredFeature<?,?> testFeature = featureRegistry.get(TEST_FEATURE);
					biomeRegistry.forEach(biome ->
					{
						// using the settings builder here is a bit chunky since it copies everything into a new list of lists
						// the biome's final feature list is an immutable list, could that be improved?
						// we could also theoretically just move the biome load event here and give it access to the dynamicregistries,
							// which would handle most use cases (adding datapack stuff to biomes)
						BiomeGenerationSettingsBuilder settingsBuilder = new BiomeGenerationSettingsBuilder(biome.getGenerationSettings());
						// add the feature to the biome
						settingsBuilder.addFeature(Decoration.VEGETAL_DECORATION, testFeature);
						((BiomeAccessor)(Object)biome).setGenerationSettings(settingsBuilder.build());
					});
				}));
	}
	
	public static class DynamicRegistriesLoadedEvent extends Event
	{
		private final @Nonnull DynamicRegistries.Impl registries;
		
		public DynamicRegistriesLoadedEvent(final @Nonnull DynamicRegistries.Impl registries)
		{
			this.registries = registries;
		}
		
		public @Nonnull DynamicRegistries.Impl getRegistries()
		{
			return this.registries;
		}
	}

}

test_pile.json

{
	"config": 
	{
		"feature": 
		{
			"config": 
			{
				"feature": 
				{
					"config": 
					{
						"state_provider": 
						{
							"state": 
							{
								"Name": "minecraft:gold_block"
							},
							"type": "minecraft:simple_state_provider"
						}
					},
					"type": "minecraft:block_pile"
				},
				"decorator": 
				{
					"config": 
					{
						"outer": 
						{
							"config": 
							{
							},
							"type": "minecraft:square"
						},
						"inner": 
						{
							"config": 
							{
							},
							"type": "minecraft:heightmap"
						}
					},
					"type": "minecraft:decorated"
				}
			},
			"type": "minecraft:decorated"
		},
		"decorator": 
		{
			"config": 
			{
				"count": 
				{
					"base": 10,
					"spread": 20
				}
			},
			"type": "minecraft:count"
		}
	},
	"type": "minecraft:decorated"
}

WorldSettingsImportMixin.java

package commoble.dynamicregistrycheeser.mixin;

import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;

import com.mojang.serialization.DynamicOps;

import commoble.dynamicregistrycheeser.DynamicRegistryCheeser.DynamicRegistriesLoadedEvent;
import net.minecraft.resources.IResourceManager;
import net.minecraft.util.registry.DynamicRegistries;
import net.minecraft.util.registry.WorldSettingsImport;
import net.minecraftforge.common.MinecraftForge;

@Mixin(WorldSettingsImport.class)
public class WorldSettingsImportMixin
{
	@SuppressWarnings("rawtypes")
	@Inject(method="create", at=@At("TAIL"))
	private static void onCreateFromResourceManager(DynamicOps ops, IResourceManager manager, DynamicRegistries.Impl registries, CallbackInfoReturnable<WorldSettingsImport> ci)
	{
		MinecraftForge.EVENT_BUS.post(new DynamicRegistriesLoadedEvent(registries));
	}
}