Make getKnockbackResistance() work for all materials (#2129)

* Make getKnockbackResistance() work for all materials

* Add missing license to ArmorItemMixin.java

* Fix all build failures

* Document ArmorItemMixin

fabric-item-api-v1/src/main/java/net/fabricmc/fabric/mixin/item/ArmorItemMixin.java

@@ -0,0 +1,55 @@
+/*
+ * 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.item;
+
+import java.util.UUID;
+
+import com.google.common.collect.ImmutableMultimap;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyVariable;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+
+import net.minecraft.entity.attribute.EntityAttributeModifier;
+import net.minecraft.entity.attribute.EntityAttributes;
+import net.minecraft.entity.attribute.EntityAttribute;
+import net.minecraft.entity.EquipmentSlot;
+import net.minecraft.item.ArmorItem;
+import net.minecraft.item.ArmorMaterial;
+import net.minecraft.item.ArmorMaterials;
+
+@Mixin(ArmorItem.class)
+public class ArmorItemMixin {
+	@Shadow private static @Final UUID[] MODIFIERS;
+	@Shadow protected @Final float knockbackResistance;
+
+	/* Vanilla only adds a knockback resistance modifier to ArmorItems made of ArmorMaterials.NETHERITE. This mixin
+	 * adds a knockback resistance modifier to any ArmorItem if knockbackResistance is > 0.0F.
+	 */
+	@ModifyVariable(method = "<init>", at = @At(value = "INVOKE", target = "Lcom/google/common/collect/ImmutableMultimap$Builder;build()Lcom/google/common/collect/ImmutableMultimap;"))
+	private ImmutableMultimap.Builder<EntityAttribute, EntityAttributeModifier> fabric_knockbackResistance(ImmutableMultimap.Builder<EntityAttribute, EntityAttributeModifier> builder, ArmorMaterial material, EquipmentSlot slot) {
+		// Vanilla handles netherite
+		if (material != ArmorMaterials.NETHERITE && knockbackResistance > 0.0F) {
+			builder.put(EntityAttributes.GENERIC_KNOCKBACK_RESISTANCE, new EntityAttributeModifier(
+					MODIFIERS[slot.getEntitySlotId()], "Armor knockback resistance",
+					knockbackResistance, EntityAttributeModifier.Operation.ADDITION));
+		}
+
+		return builder;
+	}
+}

fabric-item-api-v1/src/main/resources/fabric-item-api-v1.mixins.json

@@ -5,7 +5,8 @@
   "mixins": [
     "ItemStackMixin",
     "ItemMixin",
-    "LivingEntityMixin"
+    "LivingEntityMixin",
+    "ArmorItemMixin"
   ],
   "client": [
     "client.ClientPlayerInteractionManagerMixin",

fabric-item-api-v1/src/testmod/java/net/fabricmc/fabric/test/item/ArmorKnockbackResistanceTest.java

@@ -0,0 +1,80 @@
+/*
+ * 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.item;
+
+import net.minecraft.entity.EquipmentSlot;
+import net.minecraft.item.ArmorItem;
+import net.minecraft.item.ArmorMaterial;
+import net.minecraft.item.Item;
+import net.minecraft.recipe.Ingredient;
+import net.minecraft.sound.SoundEvent;
+import net.minecraft.sound.SoundEvents;
+import net.minecraft.tag.ItemTags;
+import net.minecraft.util.Identifier;
+import net.minecraft.util.registry.Registry;
+
+import net.fabricmc.api.ModInitializer;
+
+public class ArmorKnockbackResistanceTest implements ModInitializer {
+	private static final ArmorMaterial WOOD_ARMOR = new ArmorMaterial() {
+		@Override
+		public int getDurability(EquipmentSlot slot) {
+			return 50;
+		}
+
+		@Override
+		public int getProtectionAmount(EquipmentSlot slot) {
+			return 5;
+		}
+
+		@Override
+		public int getEnchantability() {
+			return 1;
+		}
+
+		@Override
+		public SoundEvent getEquipSound() {
+			return SoundEvents.ITEM_ARMOR_EQUIP_GENERIC;
+		}
+
+		@Override
+		public Ingredient getRepairIngredient() {
+			return Ingredient.fromTag(ItemTags.LOGS);
+		}
+
+		@Override
+		public String getName() {
+			return "wood";
+		}
+
+		@Override
+		public float getToughness() {
+			return 0.0F;
+		}
+
+		@Override
+		public float getKnockbackResistance() {
+			return 0.5F;
+		}
+	};
+
+	@Override
+	public void onInitialize() {
+		Registry.register(Registry.ITEM, new Identifier("fabric-item-api-v1-testmod",
+				"wooden_boots"), new ArmorItem(WOOD_ARMOR, EquipmentSlot.FEET, new Item.Settings()));
+	}
+}

fabric-item-api-v1/src/testmod/resources/assets/fabric-item-api-v1-testmod/models/item/wooden_boots.json

@@ -0,0 +1,8 @@
+{
+  "parent": "minecraft:item/generated",
+  "textures": {
+    "layer0": "minecraft:block/oak_log",
+    "layer1": "minecraft:item/leather_boots",
+    "layer2": "minecraft:item/leather_boots_overlay"
+  }
+}

fabric-item-api-v1/src/testmod/resources/fabric.mod.json

@@ -13,7 +13,8 @@
       "net.fabricmc.fabric.test.item.CustomDamageTest",
       "net.fabricmc.fabric.test.item.FabricItemSettingsTests",
       "net.fabricmc.fabric.test.item.ItemUpdateAnimationTest",
-      "net.fabricmc.fabric.test.item.ModifyItemAttributeModifiersCallbackTest"
+      "net.fabricmc.fabric.test.item.ModifyItemAttributeModifiersCallbackTest",
+      "net.fabricmc.fabric.test.item.ArmorKnockbackResistanceTest"
     ],
     "client": [
       "net.fabricmc.fabric.test.item.client.TooltipTests"