Add loot modifiers

fabric-data-generation-api-v1/build.gradle

@@ -10,6 +10,7 @@ moduleDependencies(project, [
 
 testDependencies(project, [
 	':fabric-item-group-api-v1',
+	':fabric-loot-api-v3',
     ':fabric-object-builder-api-v1'
 ])
 

fabric-data-generation-api-v1/src/testmod/generated/data/fabric-data-gen-api-v1-testmod/fabric/loot_modifier/modifier_a.json

@@ -0,0 +1,34 @@
+{
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:survives_explosion"
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:apple"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "target": {
+    "type": "fabric:require_all",
+    "children": [
+      {
+        "type": "fabric:source",
+        "sources": "any_builtin"
+      },
+      {
+        "type": "fabric:loot_table_id",
+        "loot_tables": [
+          "minecraft:blocks/acacia_button"
+        ]
+      }
+    ]
+  }
+}

fabric-data-generation-api-v1/src/testmod/generated/data/fabric-data-gen-api-v1-testmod/fabric/loot_modifier/modifier_b.json

@@ -0,0 +1,54 @@
+{
+  "functions": [
+    {
+      "add": false,
+      "count": 10.0,
+      "function": "minecraft:set_count"
+    }
+  ],
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:survives_explosion"
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:golden_apple"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "target": {
+    "type": "fabric:require_any",
+    "children": [
+      {
+        "type": "fabric:loot_table_id",
+        "loot_tables": [
+          "minecraft:blocks/anvil"
+        ]
+      },
+      {
+        "type": "fabric:require_all",
+        "children": [
+          {
+            "type": "fabric:loot_table_id",
+            "loot_tables": [
+              "minecraft:entities/allay"
+            ]
+          },
+          {
+            "type": "fabric:source",
+            "sources": [
+              "data_pack"
+            ]
+          }
+        ]
+      }
+    ]
+  }
+}

fabric-data-generation-api-v1/src/testmod/java/net/fabricmc/fabric/test/datagen/DataGeneratorTestEntrypoint.java

@@ -77,7 +77,9 @@
 import net.minecraft.world.level.storage.loot.LootPool;
 import net.minecraft.world.level.storage.loot.LootTable;
 import net.minecraft.world.level.storage.loot.entries.LootItem;
+import net.minecraft.world.level.storage.loot.functions.SetItemCountFunction;
 import net.minecraft.world.level.storage.loot.parameters.LootContextParamSets;
+import net.minecraft.world.level.storage.loot.predicates.ExplosionCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemBlockStatePropertyCondition;
 import net.minecraft.world.level.storage.loot.predicates.LootItemCondition;
 import net.minecraft.world.level.storage.loot.providers.number.ConstantValue;
@@ -96,6 +98,9 @@
 import net.fabricmc.fabric.api.datagen.v1.provider.FabricRecipeProvider;
 import net.fabricmc.fabric.api.datagen.v1.provider.FabricTagProvider;
 import net.fabricmc.fabric.api.datagen.v1.provider.SimpleFabricLootTableProvider;
+import net.fabricmc.fabric.api.loot.v3.LootModifier;
+import net.fabricmc.fabric.api.loot.v3.LootModifierTarget;
+import net.fabricmc.fabric.api.loot.v3.LootTableSource;
 import net.fabricmc.fabric.api.recipe.v1.ingredient.DefaultCustomIngredients;
 import net.fabricmc.fabric.api.resource.conditions.v1.ResourceCondition;
 import net.fabricmc.fabric.api.resource.conditions.v1.ResourceConditions;
@@ -123,6 +128,7 @@ public void onInitializeDataGenerator(FabricDataGenerator dataGenerator) {
 		pack.addProvider(JapaneseLangProvider::new);
 		pack.addProvider(TestDynamicRegistryProvider::new);
 		pack.addProvider(TestPredicateProvider::new);
+		pack.addProvider(TestLootModifierProvider::new);
 		pack.addProvider(TestCustomCodecProvider::new);
 
 		TestBlockTagProvider blockTagProvider = pack.addProvider(TestBlockTagProvider::new);
@@ -496,6 +502,44 @@ public String getName() {
 		}
 	}
 
+	private static class TestLootModifierProvider extends FabricCodecDataProvider<LootModifier> {
+		private TestLootModifierProvider(FabricDataOutput dataOutput, CompletableFuture<HolderLookup.Provider> registriesFuture) {
+			super(dataOutput, registriesFuture, PackOutput.Target.DATA_PACK, LootModifier.DATA_DIRECTORY, LootModifier.CODEC);
+		}
+
+		@Override
+		protected void configure(BiConsumer<Identifier, LootModifier> provider, HolderLookup.Provider lookup) {
+			LootModifier modifierA = LootModifier.builder()
+					.target(LootModifierTarget.all(LootModifierTarget.builtinSource(), LootModifierTarget.lootTable(net.minecraft.world.level.block.Blocks.ACACIA_BUTTON.getLootTable().orElseThrow())))
+					.pools(LootPool.lootPool()
+							.add(LootItem.lootTableItem(Items.APPLE))
+							.when(ExplosionCondition.survivesExplosion())
+							.build())
+					.build();
+			LootModifier modifierB = LootModifier.builder()
+					.target(LootModifierTarget.any(
+							LootModifierTarget.lootTable(net.minecraft.world.level.block.Blocks.ANVIL),
+							LootModifierTarget.all(
+									LootModifierTarget.lootTable(EntityType.ALLAY),
+									LootModifierTarget.source(LootTableSource.DATA_PACK)
+							)
+					))
+					.pools(LootPool.lootPool()
+							.add(LootItem.lootTableItem(Items.GOLDEN_APPLE))
+							.when(ExplosionCondition.survivesExplosion()))
+					.functions(SetItemCountFunction.setCount(ConstantValue.exactly(10)))
+					.build();
+
+			provider.accept(Identifier.fromNamespaceAndPath(MOD_ID, "modifier_a"), modifierA);
+			provider.accept(Identifier.fromNamespaceAndPath(MOD_ID, "modifier_b"), modifierB);
+		}
+
+		@Override
+		public String getName() {
+			return "Loot Modifiers";
+		}
+	}
+
 	private static class TestCustomCodecProvider extends FabricCodecDataProvider<TestCustomCodecProvider.Entry> {
 		private TestCustomCodecProvider(FabricDataOutput dataOutput, CompletableFuture<HolderLookup.Provider> registriesFuture) {
 			super(dataOutput, registriesFuture, PackOutput.Target.DATA_PACK, "biome_entry", Entry.CODEC);

fabric-loot-api-v3/build.gradle

@@ -2,5 +2,6 @@ version = getSubprojectVersion(project)
 
 moduleDependencies(project, [
 	'fabric-api-base',
+	'fabric-registry-sync-v0',
 	'fabric-resource-loader-v0'
 ])

fabric-loot-api-v3/src/main/java/net/fabricmc/fabric/api/loot/v3/LootModifier.java

@@ -0,0 +1,164 @@
+package net.fabricmc.fabric.api.loot.v3;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.Objects;
+
+import com.mojang.serialization.Codec;
+import org.jetbrains.annotations.ApiStatus;
+import org.jspecify.annotations.Nullable;
+
+import net.minecraft.world.level.storage.loot.LootPool;
+import net.minecraft.world.level.storage.loot.functions.LootItemFunction;
+
+import net.fabricmc.fabric.impl.loot.LootModifierImpl;
+
+/**
+ * A data-driven modifier for loot tables.
+ * Loot modifiers can add new {@linkplain LootPool pools} and {@linkplain LootItemFunction functions}
+ * to loot tables without overriding loot table data files.
+ *
+ * <p>Loot modifiers can be defined in the {@link #DATA_DIRECTORY data/[namespace]/fabric/loot_modifier}
+ * directory as JSON files with the following format: TODO add format
+ * {@snippet lang=json :
+ * "something"
+ * }
+ * You can also generate loot modifier files using {@link net.fabricmc.fabric.api.datagen.v1.provider.FabricCodecDataProvider
+ * FabricCodecDataProvider}.
+ * New modifiers can be created with a {@linkplain #builder() builder}.
+ *
+ * <p>Loot modifiers determine which loot tables they modify by using a {@link LootModifierTarget}.
+ * You can use them to target specific loot tables or only builtin loot tables, just like with {@link LootTableEvents#MODIFY}.
+ */
+@ApiStatus.NonExtendable
+public interface LootModifier {
+	/**
+	 * The data directory for loot modifiers.
+	 */
+	String DATA_DIRECTORY = "fabric/loot_modifier";
+
+	/**
+	 * The loot modifier codec.
+	 */
+	Codec<LootModifier> CODEC = LootModifierImpl.CODEC;
+
+	/**
+	 * {@return the target of this loot modifier}
+	 */
+	LootModifierTarget target();
+
+	/**
+	 * {@return the pools added by this loot modifier}
+	 */
+	List<LootPool> pools();
+
+	/**
+	 * {@return the functions added by this loot modifier}
+	 */
+	List<LootItemFunction> functions();
+
+	/**
+	 * {@return a new loot modifier builder}
+	 */
+	static Builder builder() {
+		return new Builder();
+	}
+
+	/**
+	 * A builder for {@link LootModifier}.
+	 */
+	final class Builder {
+		private @Nullable LootModifierTarget target;
+		private final List<LootPool> pools = new ArrayList<>();
+		private final List<LootItemFunction> functions = new ArrayList<>();
+
+		/**
+		 * Sets the loot modifier target.
+		 *
+		 * @param target the target
+		 * @return this builder
+		 */
+		public Builder target(LootModifierTarget target) {
+			Objects.requireNonNull(target, "Loot modifier target cannot be null");
+			this.target = target;
+			return this;
+		}
+
+		/**
+		 * Adds pools to this builder.
+		 *
+		 * @param pools the pools to add
+		 * @return this builder
+		 */
+		public Builder pools(LootPool.Builder... pools) {
+			return pools(Arrays.stream(pools).map(LootPool.Builder::build).toList());
+		}
+
+		/**
+		 * Adds pools to this builder.
+		 *
+		 * @param pools the pools to add
+		 * @return this builder
+		 */
+		public Builder pools(LootPool... pools) {
+			return pools(Arrays.asList(pools));
+		}
+
+		/**
+		 * Adds pools to this builder.
+		 *
+		 * @param pools the pools to add
+		 * @return this builder
+		 */
+		public Builder pools(Collection<? extends LootPool> pools) {
+			this.pools.addAll(pools);
+			return this;
+		}
+
+		/**
+		 * Adds functions to this builder.
+		 *
+		 * @param functions the functions to add
+		 * @return this builder
+		 */
+		public Builder functions(LootItemFunction.Builder... functions) {
+			return functions(Arrays.stream(functions).map(LootItemFunction.Builder::build).toList());
+		}
+
+		/**
+		 * Adds functions to this builder.
+		 *
+		 * @param functions the functions to add
+		 * @return this builder
+		 */
+		public Builder functions(LootItemFunction... functions) {
+			return functions(Arrays.asList(functions));
+		}
+
+		/**
+		 * Adds functions to this builder.
+		 *
+		 * @param functions the functions to add
+		 * @return this builder
+		 */
+		public Builder functions(Collection<? extends LootItemFunction> functions) {
+			this.functions.addAll(functions);
+			return this;
+		}
+
+		// TODO: test datagenning
+
+		/**
+		 * Builds a loot modifier from this builder.
+		 *
+		 * @return the created modifier
+		 * @throws NullPointerException if the target hasn't been set
+		 */
+		public LootModifier build() {
+			Objects.requireNonNull(target, "Loot modifier target not set");
+			return new LootModifierImpl(target, pools, functions);
+		}
+	}
+}