Fix the issue of uninstalling a dimension mod or datapack (#2078)

* Fix the vanilla bug of uninstalling dimensions.

* fix license

* fix style

* Rename LevelStorageMixin and some minor changes.

(cherry picked from commit 01a4d43dcd)

fabric-dimensions-v1/src/main/java/net/fabricmc/fabric/mixin/dimension/LevelStorageBugfixMixin.java

@@ -0,0 +1,83 @@
+/*
+ * 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.dimension;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+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.datafixers.DataFixer;
+import com.mojang.datafixers.util.Pair;
+import com.mojang.serialization.Dynamic;
+import com.mojang.serialization.Lifecycle;
+
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.nbt.NbtElement;
+import net.minecraft.world.gen.GeneratorOptions;
+import net.minecraft.world.level.storage.LevelStorage;
+
+/**
+ * After removing a dimension mod or a dimension datapack, Minecraft may fail to enter
+ * the world, because it fails to deserialize the chunk generator of the custom dimensions in file {@code level.dat}
+ * This mixin will remove the custom dimensions from the nbt tag, so the deserializer and DFU cannot see custom
+ * dimensions and won't cause errors.
+ * The custom dimensions will be re-added later.
+ *
+ * <p>This Mixin changes a vanilla behavior that is deemed as a bug (MC-197860). In vanilla, the custom dimension
+ * is not removed after uninstalling the dimension datapack.
+ * This makes custom dimensions non-removable. Most players don't want this behavior.
+ * With this Mixin, custom dimensions will be removed when its datapack is removed.
+ */
+@Mixin(LevelStorage.class)
+public class LevelStorageBugfixMixin {
+	@SuppressWarnings("unchecked")
+	@Inject(method = "readGeneratorProperties", at = @At("HEAD"))
+	private static <T> void onReadGeneratorProperties(
+			Dynamic<T> nbt, DataFixer dataFixer, int version,
+			CallbackInfoReturnable<Pair<GeneratorOptions, Lifecycle>> cir
+	) {
+		NbtElement nbtTag = ((Dynamic<NbtElement>) nbt).getValue();
+
+		NbtCompound worldGenSettings = ((NbtCompound) nbtTag).getCompound("WorldGenSettings");
+
+		removeNonVanillaDimensionsFromWorldGenSettingsTag(worldGenSettings);
+	}
+
+	/**
+	 * Removes all non-vanilla dimensions from the tag. The custom dimensions will be re-added later from the datapacks.
+	 */
+	@Unique
+	private static void removeNonVanillaDimensionsFromWorldGenSettingsTag(NbtCompound worldGenSettings) {
+		String[] vanillaDimensionIds =
+				new String[]{"minecraft:overworld", "minecraft:the_nether", "minecraft:the_end"};
+
+		NbtCompound dimensions = worldGenSettings.getCompound("dimensions");
+
+		if (dimensions.getSize() > vanillaDimensionIds.length) {
+			NbtCompound newDimensions = new NbtCompound();
+
+			for (String dimId : vanillaDimensionIds) {
+				if (dimensions.contains(dimId)) {
+					newDimensions.put(dimId, dimensions.getCompound(dimId));
+				}
+			}
+
+			worldGenSettings.put("dimensions", newDimensions);
+		}
+	}
+}

fabric-dimensions-v1/src/main/resources/fabric-dimensions-v1.mixins.json

@@ -4,8 +4,9 @@
   "compatibilityLevel": "JAVA_16",
   "mixins": [
     "EntityMixin",
-    "ServerPlayerEntityMixin",
-    "ServerBugfixMixin"
+    "LevelStorageBugfixMixin",
+    "ServerBugfixMixin",
+    "ServerPlayerEntityMixin"
   ],
   "injectors": {
     "defaultRequire": 1