Add missing ItemStack mixin

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

@@ -0,0 +1,28 @@
+/*
+ * 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 net.fabricmc.fabric.api.item.v1.FabricItemStack;
+
+import net.minecraft.item.ItemStack;
+
+import org.spongepowered.asm.mixin.Mixin;
+
+@Mixin(ItemStack.class)
+public abstract class ItemStackMixin implements FabricItemStack {
+
+}

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

@@ -3,7 +3,8 @@
   "package": "net.fabricmc.fabric.mixin.item",
   "compatibilityLevel": "JAVA_16",
   "mixins": [
-    "ItemMixin"
+    "ItemMixin",
+    "ItemStackMixin"
   ],
   "injectors": {
     "defaultRequire": 1

gradle.properties

@@ -67,4 +67,4 @@ fabric-client-tags-api-v1-version=1.1.1
 loom.platform=forge
 forge_version=1.20.1-47.1.3
 pack_format=15
-forgified_version=1.6.0
+forgified_version=1.6.1