Resource loader changes and built-in mod resource/data packs API (#1011)

* WIP built-in resource packs API.

* Add built-in resource pack register API and fix old injection methods.

* Fix code style.

* Fix code style.

* Add documentation.

* Drop useless else.

* Fix resource packs and data packs isolation issues, and more.

* Move ResourcePackManagerAccessor to its own accessor mixin.

* Make the built-in mod pack test mod work on server too because data pack part.

* Add new argument to built-in pack method and make mod data packs always active.

* Add documentation.

* Complete documentation in GameOptions mixin.

* Remove register built-in pack overload as Player requested.

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/api/resource/ResourceManagerHelper.java

@@ -18,8 +18,10 @@ package net.fabricmc.fabric.api.resource;
 
 import net.minecraft.resource.ResourceManager;
 import net.minecraft.resource.ResourceType;
+import net.minecraft.util.Identifier;
 
 import net.fabricmc.fabric.impl.resource.loader.ResourceManagerHelperImpl;
+import net.fabricmc.loader.api.ModContainer;
 
 /**
  * Helper for working with {@link ResourceManager} instances.
@@ -52,4 +54,27 @@ public interface ResourceManagerHelper {
 	static ResourceManagerHelper get(ResourceType type) {
 		return ResourceManagerHelperImpl.get(type);
 	}
+
+	/**
+	 * Registers a built-in resource pack.
+	 *
+	 * <p>A built-in resource pack is an extra resource pack provided by your mod which is not always active, it's similar to the "Programmer Art" resource pack.
+	 *
+	 * <p>Why and when to use it? A built-in resource pack should be used to provide extra assets/data that should be optional with your mod but still directly provided by it.
+	 * For example it could provide textures of your mod in another resolution, or could allow to provide different styles of your assets.
+	 *
+	 * <p>The {@code subPath} corresponds to a path in the JAR file which points to the resource pack folder. For example the subPath can be {@code "resourcepacks/extra"}.
+	 *
+	 * <p>Note about the enabled by default parameter: a resource pack cannot be enabled by default, only data packs can.
+	 * Making this work for resource packs is near impossible without touching how Vanilla handles disabled resource packs.
+	 *
+	 * @param id The identifier of the resource pack.
+	 * @param subPath The sub path in the mod resources.
+	 * @param container The mod container.
+	 * @param enabledByDefault True if enabled by default, else false.
+	 * @return True if successfully registered the resource pack, else false.
+	 */
+	static boolean registerBuiltinResourcePack(Identifier id, String subPath, ModContainer container, boolean enabledByDefault) {
+		return ResourceManagerHelperImpl.registerBuiltinResourcePack(id, subPath, container, enabledByDefault);
+	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/impl/resource/loader/ModNioResourcePack.java

@@ -50,14 +50,19 @@ public class ModNioResourcePack extends AbstractFileResourcePack implements ModR
 	private final boolean cacheable;
 	private final AutoCloseable closer;
 	private final String separator;
+	private final String name;
+	private final boolean defaultEnabled;
 
-	public ModNioResourcePack(ModMetadata modInfo, Path path, AutoCloseable closer) {
+	public ModNioResourcePack(ModMetadata modInfo, Path path, AutoCloseable closer, String name, boolean defaultEnabled) {
 		super(null);
 		this.modInfo = modInfo;
 		this.basePath = path.toAbsolutePath().normalize();
 		this.cacheable = false; /* TODO */
 		this.closer = closer;
 		this.separator = basePath.getFileSystem().getSeparator();
+		// Specific to registered built-in resource packs.
+		this.name = name;
+		this.defaultEnabled = defaultEnabled;
 	}
 
 	private Path getPath(String filename) {
@@ -225,8 +230,16 @@ public class ModNioResourcePack extends AbstractFileResourcePack implements ModR
 		return modInfo;
 	}
 
+	public boolean shouldBeEnabledByDefault() {
+		return this.defaultEnabled;
+	}
+
 	@Override
 	public String getName() {
+		if (this.name != null) {
+			return this.name; // Built-in resource pack provided by a mod, the name is overriden.
+		}
+
 		return ModResourcePackUtil.getName(modInfo);
 	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/impl/resource/loader/ModResourcePackCreator.java

@@ -29,8 +29,12 @@ import net.minecraft.text.TranslatableText;
 
 import net.fabricmc.fabric.api.resource.ModResourcePack;
 
+/**
+ * Represents a resource pack provider for mods and built-in mods resource packs.
+ */
 public class ModResourcePackCreator implements ResourcePackProvider {
 	public static final ResourcePackSource RESOURCE_PACK_SOURCE = text -> new TranslatableText("pack.nameAndSource", text, new TranslatableText("pack.source.fabricmod"));
+	public static final ModResourcePackCreator CLIENT_RESOURCE_PACK_PROVIDER = new ModResourcePackCreator(ResourceType.CLIENT_RESOURCES);
 	private final ResourceType type;
 
 	public ModResourcePackCreator(ResourceType type) {
@@ -39,7 +43,19 @@ public class ModResourcePackCreator implements ResourcePackProvider {
 
 	@Override
 	public void register(Consumer<ResourcePackProfile> consumer, ResourcePackProfile.Factory factory) {
-		// TODO: "vanilla" does not emit a message; neither should a modded datapack
+		/*
+			Register order rule in this provider:
+			1. Mod resource packs
+			2. Mod built-in resource packs
+
+			Register order rule globally:
+			1. Default and Vanilla built-in resource packs
+			2. Mod resource packs
+			3. Mod built-in resource packs
+			4. User resource packs
+		 */
+
+		// Build a list of mod resource packs.
 		List<ResourcePack> packs = new ArrayList<>();
 		ModResourcePackUtil.appendModResourcePacks(packs, type);
 
@@ -48,13 +64,19 @@ public class ModResourcePackCreator implements ResourcePackProvider {
 				throw new RuntimeException("Not a ModResourcePack!");
 			}
 
+			// Make the resource pack profile for mod resource packs.
+			// Mod resource packs must always be enabled to avoid issues
+			// and inserted on top to ensure that they are applied before user resource packs and after default/programmer art resource pack.
 			ResourcePackProfile resourcePackProfile = ResourcePackProfile.of("fabric/" + ((ModResourcePack) pack).getFabricModMetadata().getId(),
-					false, () -> pack, factory, ResourcePackProfile.InsertionPosition.TOP,
+					true, () -> pack, factory, ResourcePackProfile.InsertionPosition.TOP,
 					RESOURCE_PACK_SOURCE);
 
 			if (resourcePackProfile != null) {
 				consumer.accept(resourcePackProfile);
 			}
 		}
+
+		// Register all built-in resource packs provided by mods.
+		ResourceManagerHelperImpl.registerBuiltinResourcePacks(this.type, consumer, factory);
 	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/impl/resource/loader/ModResourcePackUtil.java

@@ -21,16 +21,12 @@ import java.nio.file.Path;
 import java.util.List;
 
 import com.google.common.base.Charsets;
-import com.google.common.collect.Lists;
 import org.apache.commons.io.IOUtils;
 
 import net.minecraft.SharedConstants;
-import net.minecraft.client.resource.Format4ResourcePack;
 import net.minecraft.resource.ResourcePack;
 import net.minecraft.resource.ResourceType;
-import net.minecraft.resource.DefaultResourcePack;
 
-import net.fabricmc.fabric.mixin.resource.loader.MixinFormat4ResourcePack;
 import net.fabricmc.loader.api.FabricLoader;
 import net.fabricmc.loader.api.ModContainer;
 import net.fabricmc.loader.api.metadata.ModMetadata;
@@ -50,7 +46,7 @@ public final class ModResourcePackUtil {
 			}
 
 			Path path = container.getRootPath();
-			ResourcePack pack = new ModNioResourcePack(container.getMetadata(), path, null);
+			ResourcePack pack = new ModNioResourcePack(container.getMetadata(), path, null, null, true);
 
 			if (!pack.getNamespaces(type).isEmpty()) {
 				packList.add(pack);
@@ -87,38 +83,4 @@ public final class ModResourcePackUtil {
 			return "Fabric Mod \"" + info.getId() + "\"";
 		}
 	}
-
-	public static void modifyResourcePackList(List<ResourcePack> list) {
-		List<ResourcePack> oldList = Lists.newArrayList(list);
-		list.clear();
-
-		boolean appended = false;
-
-		for (int i = 0; i < oldList.size(); i++) {
-			ResourcePack pack = oldList.get(i);
-			list.add(pack);
-
-			boolean isDefaultResources = pack instanceof DefaultResourcePack;
-
-			if (!isDefaultResources && pack instanceof Format4ResourcePack) {
-				MixinFormat4ResourcePack fixer = (MixinFormat4ResourcePack) pack;
-				isDefaultResources = fixer.getParent() instanceof DefaultResourcePack;
-			}
-
-			if (isDefaultResources) {
-				ModResourcePackUtil.appendModResourcePacks(list, ResourceType.CLIENT_RESOURCES);
-				appended = true;
-			}
-		}
-
-		if (!appended) {
-			StringBuilder builder = new StringBuilder("Fabric could not find resource pack injection location!");
-
-			for (ResourcePack rp : oldList) {
-				builder.append("\n - ").append(rp.getName()).append(" (").append(rp.getClass().getName()).append(")");
-			}
-
-			throw new RuntimeException(builder.toString());
-		}
-	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/impl/resource/loader/ResourceManagerHelperImpl.java

@@ -16,6 +16,8 @@
 
 package net.fabricmc.fabric.impl.resource.loader;
 
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -23,20 +25,26 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Consumer;
 
 import com.google.common.collect.Lists;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+import net.minecraft.resource.ResourcePackProfile;
+import net.minecraft.resource.ResourcePackSource;
 import net.minecraft.resource.ResourceReloadListener;
 import net.minecraft.resource.ResourceType;
 import net.minecraft.util.Identifier;
+import net.minecraft.util.Pair;
 
+import net.fabricmc.loader.api.ModContainer;
 import net.fabricmc.fabric.api.resource.IdentifiableResourceReloadListener;
 import net.fabricmc.fabric.api.resource.ResourceManagerHelper;
 
 public class ResourceManagerHelperImpl implements ResourceManagerHelper {
 	private static final Map<ResourceType, ResourceManagerHelperImpl> registryMap = new HashMap<>();
+	private static final Set<Pair<String, ModNioResourcePack>> builtinResourcePacks = new HashSet<>();
 	private static final Logger LOGGER = LogManager.getLogger();
 
 	private final Set<Identifier> addedListenerIds = new HashSet<>();
@@ -46,6 +54,48 @@ public class ResourceManagerHelperImpl implements ResourceManagerHelper {
 		return registryMap.computeIfAbsent(type, (t) -> new ResourceManagerHelperImpl());
 	}
 
+	/**
+	 * Registers a built-in resource pack. Internal implementation.
+	 *
+	 * @param id The identifier of the resource pack.
+	 * @param subPath The sub path in the mod resources.
+	 * @param container The mod container.
+	 * @param enabledByDefault True if enabled by default, else false.
+	 * @return True if successfully registered the resource pack, else false.
+	 *
+	 * @see ResourceManagerHelper#registerBuiltinResourcePack(Identifier, String, ModContainer, boolean)
+	 */
+	public static boolean registerBuiltinResourcePack(Identifier id, String subPath, ModContainer container, boolean enabledByDefault) {
+		String separator = container.getRootPath().getFileSystem().getSeparator();
+		subPath = subPath.replace("/", separator);
+
+		Path resourcePackPath = container.getRootPath().resolve(subPath).toAbsolutePath().normalize();
+
+		if (!Files.exists(resourcePackPath)) {
+			return false;
+		}
+
+		String name = id.getNamespace() + "/" + id.getPath();
+		builtinResourcePacks.add(new Pair<>(name, new ModNioResourcePack(container.getMetadata(), resourcePackPath, null, name, enabledByDefault)));
+
+		return true;
+	}
+
+	public static void registerBuiltinResourcePacks(ResourceType resourceType, Consumer<ResourcePackProfile> consumer, ResourcePackProfile.Factory factory) {
+		// Loop through each registered built-in resource packs and add them if valid.
+		for (Pair<String, ModNioResourcePack> entry : builtinResourcePacks) {
+			// Add the built-in pack only if namespaces for the specified resource type are present.
+			if (!entry.getRight().getNamespaces(resourceType).isEmpty()) {
+				// Make the resource pack profile for built-in pack, should never be always enabled.
+				ResourcePackProfile profile = ResourcePackProfile.of(entry.getLeft(), false,
+						entry::getRight, factory, ResourcePackProfile.InsertionPosition.TOP, ResourcePackSource.PACK_SOURCE_BUILTIN);
+				if (profile != null) {
+					consumer.accept(profile);
+				}
+			}
+		}
+	}
+
 	public static void sort(ResourceType type, List<ResourceReloadListener> listeners) {
 		ResourceManagerHelperImpl instance = registryMap.get(type);
 

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/FileResourcePackProviderAccessor.java

@@ -19,11 +19,11 @@ package net.fabricmc.fabric.mixin.resource.loader;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.gen.Accessor;
 
-import net.minecraft.client.resource.Format4ResourcePack;
-import net.minecraft.resource.ResourcePack;
+import net.minecraft.resource.FileResourcePackProvider;
+import net.minecraft.resource.ResourcePackSource;
 
-@Mixin(Format4ResourcePack.class)
-public interface MixinFormat4ResourcePack {
-	@Accessor
-	ResourcePack getParent();
+@Mixin(FileResourcePackProvider.class)
+public interface FileResourcePackProviderAccessor {
+	@Accessor("field_25345")
+	ResourcePackSource getResourcePackSource();
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinClientBuiltinResourcePackProvider.java

@@ -16,25 +16,23 @@
 
 package net.fabricmc.fabric.mixin.resource.loader;
 
-import java.util.ArrayList;
-import java.util.List;
+import java.util.function.Consumer;
 
 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 org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
-import net.minecraft.resource.ResourcePack;
-import net.minecraft.resource.ResourcePackManager;
+import net.minecraft.resource.ResourcePackProfile;
+import net.minecraft.client.resource.ClientBuiltinResourcePackProvider;
 
-import net.fabricmc.fabric.impl.resource.loader.ModResourcePackUtil;
+import net.fabricmc.fabric.impl.resource.loader.ModResourcePackCreator;
 
-@Mixin(ResourcePackManager.class)
-public class MixinResourcePackManagerClient {
-	@Inject(method = "createResourcePacks", at = @At("RETURN"), cancellable = true)
-	public void createResourcePacks(CallbackInfoReturnable<List<ResourcePack>> infoReturnable) {
-		List<ResourcePack> list = new ArrayList<>(infoReturnable.getReturnValue());
-		ModResourcePackUtil.modifyResourcePackList(list);
-		infoReturnable.setReturnValue(list);
+@Mixin(ClientBuiltinResourcePackProvider.class)
+public class MixinClientBuiltinResourcePackProvider {
+	@Inject(method = "register", at = @At("RETURN"))
+	private void addBuiltinResourcePacks(Consumer<ResourcePackProfile> consumer, ResourcePackProfile.Factory factory, CallbackInfo ci) {
+		// Register mod and built-in resource packs after the vanilla built-in resource packs are registered.
+		ModResourcePackCreator.CLIENT_RESOURCE_PACK_PROVIDER.register(consumer, factory);
 	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinCreateWorldScreen.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.resource.loader;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+
+import com.mojang.datafixers.util.Pair;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.ModifyArg;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import net.minecraft.client.gui.screen.world.CreateWorldScreen;
+import net.minecraft.resource.DataPackSettings;
+import net.minecraft.resource.ResourcePack;
+import net.minecraft.resource.ResourcePackManager;
+import net.minecraft.resource.ResourcePackProfile;
+import net.minecraft.resource.ResourceType;
+
+import net.fabricmc.fabric.impl.resource.loader.ModNioResourcePack;
+import net.fabricmc.fabric.impl.resource.loader.ModResourcePackCreator;
+
+@Mixin(CreateWorldScreen.class)
+public class MixinCreateWorldScreen {
+	@Shadow
+	private ResourcePackManager field_25792;
+
+	@Inject(method = "method_30296", at = @At(value = "INVOKE", target = "Lnet/minecraft/resource/ResourcePackManager;scanPacks()V", shift = At.Shift.BEFORE))
+	private void onScanPacks(CallbackInfoReturnable<Pair<File, ResourcePackManager>> cir) {
+		// Allow to display built-in data packs in the data pack selection screen at world creation.
+		((ResourcePackManagerAccessor) this.field_25792).getProviders().add(new ModResourcePackCreator(ResourceType.SERVER_DATA));
+	}
+
+	@ModifyArg(method = "method_31130", at = @At(value = "INVOKE", target = "Lnet/minecraft/client/gui/screen/world/CreateWorldScreen;<init>(Lnet/minecraft/client/gui/screen/Screen;Lnet/minecraft/resource/DataPackSettings;Lnet/minecraft/client/gui/screen/world/MoreOptionsDialog;)V"), index = 1)
+	private static DataPackSettings onNew(DataPackSettings settings) {
+		ModResourcePackCreator modResourcePackCreator = new ModResourcePackCreator(ResourceType.SERVER_DATA);
+		List<ResourcePackProfile> moddedResourcePacks = new ArrayList<>();
+		modResourcePackCreator.register(moddedResourcePacks::add, ResourcePackProfile::new);
+
+		List<String> enabled = new ArrayList<>(settings.getEnabled());
+		List<String> disabled = new ArrayList<>(settings.getDisabled());
+
+		// This ensure that any built-in registered data packs by mods which needs to be enabled by default are
+		// as the data pack screen automatically put any data pack as disabled except the Default data pack.
+		for (ResourcePackProfile profile : moddedResourcePacks) {
+			ResourcePack pack = profile.createResourcePack();
+
+			if (pack instanceof ModNioResourcePack && ((ModNioResourcePack) pack).shouldBeEnabledByDefault()) {
+				enabled.add(profile.getName());
+			} else {
+				disabled.add(profile.getName());
+			}
+		}
+
+		return new DataPackSettings(enabled, disabled);
+	}
+}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinDataPackSettings.java

@@ -1,73 +0,0 @@
-/*
- * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package net.fabricmc.fabric.mixin.resource.loader;
-
-import java.nio.file.Path;
-import java.util.ArrayList;
-import java.util.List;
-
-import org.spongepowered.asm.mixin.Final;
-import org.spongepowered.asm.mixin.Mixin;
-import org.spongepowered.asm.mixin.Mutable;
-import org.spongepowered.asm.mixin.Shadow;
-import org.spongepowered.asm.mixin.injection.At;
-import org.spongepowered.asm.mixin.injection.Inject;
-import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
-
-import net.minecraft.resource.DataPackSettings;
-import net.minecraft.resource.ResourcePack;
-import net.minecraft.resource.ResourceType;
-
-import net.fabricmc.loader.api.FabricLoader;
-import net.fabricmc.loader.api.ModContainer;
-import net.fabricmc.fabric.impl.resource.loader.ModNioResourcePack;
-
-@Mixin(DataPackSettings.class)
-public class MixinDataPackSettings {
-	@Shadow
-	@Final
-	@Mutable
-	private List<String> enabled;
-
-	/*
-	This injection takes all instances of this class with an enabled list that only have the vanilla pack enabled,
-	and forcibly enables all mod resource packs. This is probably not the best option, but it's the only one that I can
-	think of that will work on both existing and new worlds. Is there a better option?
-	 */
-	@Inject(method = "<init>", at = @At("RETURN"))
-	private void init(List<String> enabled, List<String> disabled, CallbackInfo info) {
-		if (enabled.size() == 1 && enabled.get(0).equals("vanilla")) {
-			List<String> newEnabled = new ArrayList<>(enabled);
-
-			for (ModContainer container : FabricLoader.getInstance().getAllMods()) {
-				if (container.getMetadata().getType().equals("builtin")) {
-					continue;
-				}
-
-				Path path = container.getRootPath();
-
-				try (ResourcePack pack = new ModNioResourcePack(container.getMetadata(), path, null)) {
-					if (!pack.getNamespaces(ResourceType.SERVER_DATA).isEmpty()) {
-						newEnabled.add("fabric/" + container.getMetadata().getId());
-					}
-				}
-			}
-
-			this.enabled = newEnabled;
-		}
-	}
-}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinGameOptions.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.resource.loader;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import net.minecraft.client.options.GameOptions;
+import net.minecraft.resource.ResourcePack;
+import net.minecraft.resource.ResourcePackProfile;
+
+import net.fabricmc.fabric.impl.resource.loader.ModNioResourcePack;
+import net.fabricmc.fabric.impl.resource.loader.ModResourcePackCreator;
+
+@Mixin(GameOptions.class)
+public class MixinGameOptions {
+	@Shadow
+	public List<String> resourcePacks;
+
+	@Inject(method = "load", at = @At("RETURN"))
+	private void onLoad(CallbackInfo ci) {
+		// Add built-in resource packs if they are enabled by default only if the options file is blank.
+		if (this.resourcePacks.isEmpty()) {
+			List<ResourcePackProfile> profiles = new ArrayList<>();
+			ModResourcePackCreator.CLIENT_RESOURCE_PACK_PROVIDER.register(profiles::add, ResourcePackProfile::new);
+			this.resourcePacks = new ArrayList<>();
+
+			for (ResourcePackProfile profile : profiles) {
+				ResourcePack pack = profile.createResourcePack();
+				if (profile.getSource() == ModResourcePackCreator.RESOURCE_PACK_SOURCE
+						|| (pack instanceof ModNioResourcePack && ((ModNioResourcePack) pack).shouldBeEnabledByDefault())) {
+					this.resourcePacks.add(profile.getName());
+				}
+			}
+		}
+	}
+}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinMinecraftGame.java

@@ -1,39 +0,0 @@
-/*
- * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package net.fabricmc.fabric.mixin.resource.loader;
-
-import java.util.List;
-import java.util.concurrent.CompletableFuture;
-
-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 org.spongepowered.asm.mixin.injection.callback.LocalCapture;
-
-import net.minecraft.client.MinecraftClient;
-import net.minecraft.resource.ResourcePack;
-
-import net.fabricmc.fabric.impl.resource.loader.ModResourcePackUtil;
-
-@Mixin(MinecraftClient.class)
-public class MixinMinecraftGame {
-	@Inject(method = "reloadResources", at = @At(value = "INVOKE", target = "Lnet/minecraft/resource/ReloadableResourceManager;beginMonitoredReload(Ljava/util/concurrent/Executor;Ljava/util/concurrent/Executor;Ljava/util/concurrent/CompletableFuture;Ljava/util/List;)Lnet/minecraft/resource/ResourceReloadMonitor;", ordinal = 0), locals = LocalCapture.CAPTURE_FAILHARD)
-	public void reloadResources(CallbackInfoReturnable<CompletableFuture> info, CompletableFuture<java.lang.Void> cf, List<ResourcePack> list) {
-		ModResourcePackUtil.modifyResourcePackList(list);
-	}
-}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinMinecraftServer.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.resource.loader;
+
+import java.util.List;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Redirect;
+
+import net.minecraft.resource.ResourcePack;
+import net.minecraft.resource.ResourcePackManager;
+import net.minecraft.resource.ResourcePackProfile;
+import net.minecraft.resource.ResourcePackSource;
+import net.minecraft.server.MinecraftServer;
+
+import net.fabricmc.fabric.impl.resource.loader.ModNioResourcePack;
+
+@Mixin(MinecraftServer.class)
+public class MixinMinecraftServer {
+	@Redirect(method = "loadDataPacks", at = @At(value = "INVOKE", target = "Ljava/util/List;contains(Ljava/lang/Object;)Z"))
+	private static boolean onCheckDisabled(List<String> list, Object o, ResourcePackManager resourcePackManager) {
+		String profileName = (String) o;
+		boolean contains = list.contains(profileName);
+
+		if (contains) {
+			return true;
+		}
+
+		ResourcePackProfile profile = resourcePackManager.getProfile(profileName);
+
+		if (profile.getSource() == ResourcePackSource.PACK_SOURCE_BUILTIN && !profileName.equals("vanilla")) {
+			ResourcePack pack = profile.createResourcePack();
+			// Prevents automatic load for built-in data packs provided by mods.
+			return pack instanceof ModNioResourcePack && !((ModNioResourcePack) pack).shouldBeEnabledByDefault();
+		}
+
+		return false;
+	}
+}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinPackScreen.java

@@ -21,16 +21,18 @@ import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
-import net.minecraft.client.gui.screen.pack.PackScreen;
 import net.minecraft.client.gui.screen.pack.PackListWidget;
+import net.minecraft.client.gui.screen.pack.PackScreen;
 import net.minecraft.client.gui.screen.pack.ResourcePackOrganizer;
 
 import net.fabricmc.fabric.impl.resource.loader.ModResourcePackCreator;
 
 @Mixin(PackScreen.class)
-public class MixinAbstractPackScreen {
+public class MixinPackScreen {
 	@Inject(method = "method_29672", at = @At("HEAD"), cancellable = true)
 	private void addPackEntry(PackListWidget packListWidget, ResourcePackOrganizer.Pack pack, CallbackInfo info) {
+		// Every mod resource packs should be hidden from the user.
+		// Registered built-in resource packs should not be hidden as they are optional for the user.
 		if (pack.getSource() == ModResourcePackCreator.RESOURCE_PACK_SOURCE) {
 			info.cancel();
 		}

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/MixinResourcePackManager.java

@@ -27,15 +27,17 @@ import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
+import net.minecraft.resource.FileResourcePackProvider;
 import net.minecraft.resource.ResourcePackManager;
 import net.minecraft.resource.ResourcePackProfile;
 import net.minecraft.resource.ResourcePackProvider;
+import net.minecraft.resource.ResourcePackSource;
 import net.minecraft.resource.ResourceType;
 
 import net.fabricmc.fabric.impl.resource.loader.ModResourcePackCreator;
 
 @Mixin(ResourcePackManager.class)
-public class MixinResourcePackManager<T extends ResourcePackProfile> {
+public abstract class MixinResourcePackManager<T extends ResourcePackProfile> {
 	@Shadow
 	@Final
 	@Mutable
@@ -44,6 +46,22 @@ public class MixinResourcePackManager<T extends ResourcePackProfile> {
 	@Inject(method = "<init>", at = @At("RETURN"))
 	public void construct(ResourcePackProfile.Factory arg, ResourcePackProvider[] resourcePackProviders, CallbackInfo info) {
 		providers = new HashSet<>(providers);
-		providers.add(new ModResourcePackCreator(ResourceType.SERVER_DATA));
+
+		// Search resource pack providers to find any server-related pack provider.
+		boolean shouldAddServerProvider = false;
+
+		for (ResourcePackProvider provider : this.providers) {
+			if (provider instanceof FileResourcePackProvider
+					&& (((FileResourcePackProviderAccessor) provider).getResourcePackSource() == ResourcePackSource.PACK_SOURCE_WORLD
+					|| ((FileResourcePackProviderAccessor) provider).getResourcePackSource() == ResourcePackSource.PACK_SOURCE_SERVER)) {
+				shouldAddServerProvider = true;
+				break;
+			}
+		}
+
+		// On server, add the mod resource pack provider.
+		if (shouldAddServerProvider) {
+			providers.add(new ModResourcePackCreator(ResourceType.SERVER_DATA));
+		}
 	}
 }

fabric-resource-loader-v0/src/main/java/net/fabricmc/fabric/mixin/resource/loader/ResourcePackManagerAccessor.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.resource.loader;
+
+import java.util.Set;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+
+import net.minecraft.resource.ResourcePackManager;
+import net.minecraft.resource.ResourcePackProvider;
+
+@Mixin(ResourcePackManager.class)
+public interface ResourcePackManagerAccessor {
+	/**
+	 * Returns the resource pack providers of this resource pack manager.
+	 *
+	 * @return The resource pack providers.
+	 */
+	@Accessor("providers")
+	Set<ResourcePackProvider> getProviders();
+}

fabric-resource-loader-v0/src/main/resources/fabric-resource-loader-v0.mixins.json

@@ -3,18 +3,20 @@
   "package": "net.fabricmc.fabric.mixin.resource.loader",
   "compatibilityLevel": "JAVA_8",
   "mixins": [
-    "MixinDataPackSettings",
+    "FileResourcePackProviderAccessor",
     "MixinDefaultResourcePack",
     "MixinKeyedResourceReloadListener$Server",
+    "MixinMinecraftServer",
     "MixinReloadableResourceManagerImpl",
-    "MixinResourcePackManager"
+    "MixinResourcePackManager",
+    "ResourcePackManagerAccessor"
   ],
   "client": [
-    "MixinAbstractPackScreen",
-    "MixinFormat4ResourcePack",
+    "MixinClientBuiltinResourcePackProvider",
+    "MixinCreateWorldScreen",
+    "MixinGameOptions",
     "MixinKeyedResourceReloadListener$Client",
-    "MixinMinecraftGame",
-    "MixinResourcePackManagerClient"
+    "MixinPackScreen"
   ],
   "injectors": {
     "defaultRequire": 1

fabric-resource-loader-v0/src/testmod/java/net/fabricmc/fabric/test/resource/loader/BuiltinResourcePackTestMod.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.test.resource.loader;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+import net.minecraft.util.Identifier;
+
+import net.fabricmc.api.ModInitializer;
+import net.fabricmc.fabric.api.resource.ResourceManagerHelper;
+import net.fabricmc.loader.api.FabricLoader;
+
+public class BuiltinResourcePackTestMod implements ModInitializer {
+	public static final String MODID = "fabric-resource-loader-v0-testmod";
+
+	private static final Logger LOGGER = LogManager.getLogger();
+
+	@Override
+	public void onInitialize() {
+		// Should always be present as it's **this** mod.
+		FabricLoader.getInstance().getModContainer(MODID)
+				.map(container -> ResourceManagerHelper.registerBuiltinResourcePack(new Identifier(MODID, "test"), "resourcepacks/test", container, false))
+				.filter(success -> !success).ifPresent(success -> LOGGER.warn("Could not register built-in resource pack."));
+	}
+}

fabric-resource-loader-v0/src/testmod/resources/fabric.mod.json

@@ -0,0 +1,16 @@
+{
+  "schemaVersion": 1,
+  "id": "fabric-resource-loader-v0-testmod",
+  "name": "Fabric Resource Loader (v0) Test Mod",
+  "version": "1.0.0",
+  "environment": "*",
+  "license": "Apache-2.0",
+  "depends": {
+    "fabric-resource-loader-v0": "*"
+  },
+  "entrypoints": {
+    "main": [
+      "net.fabricmc.fabric.test.resource.loader.BuiltinResourcePackTestMod"
+    ]
+  }
+}

fabric-resource-loader-v0/src/testmod/resources/resourcepacks/test/data/minecraft/tags/blocks/climbable.json

@@ -0,0 +1,6 @@
+{
+  "replace": false,
+  "values": [
+    "minecraft:bamboo"
+  ]
+}

fabric-resource-loader-v0/src/testmod/resources/resourcepacks/test/pack.mcmeta

@@ -0,0 +1,6 @@
+{
+  "pack": {
+    "pack_format": 6,
+    "description": "Fabric Resource Loader Test Builtin Pack."
+  }
+}