Skip migration for deleted dimensions post first migration in server (#13874)

Co-authored-by: Jason Penilla <11360596+jpenilla@users.noreply.github.com>

Author: Doc94

build-data/paper.at

@@ -98,6 +98,7 @@ public net.minecraft.util.Util onThreadException(Ljava/lang/Thread;Ljava/lang/Th
 public net.minecraft.util.datafix.fixes.BlockStateData register(ILcom/mojang/serialization/Dynamic;[Lcom/mojang/serialization/Dynamic;)V
 public net.minecraft.util.datafix.fixes.ItemIdFix ITEM_NAMES
 public net.minecraft.util.datafix.fixes.ItemSpawnEggFix ID_TO_ENTITY
+public net.minecraft.util.filefix.FileFixerUpper FILE_FIXER_INTRODUCTION_VERSION
 public net.minecraft.world.BossEvent color
 public net.minecraft.world.BossEvent name
 public net.minecraft.world.BossEvent overlay

paper-server/src/main/java/io/papermc/paper/world/PaperWorldLoader.java

@@ -5,8 +5,10 @@
 import io.papermc.paper.world.saveddata.PaperWorldMetadata;
 import io.papermc.paper.world.saveddata.PaperWorldPDC;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.util.Locale;
 import java.util.UUID;
+import net.minecraft.core.Registry;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.ResourceKey;
 import net.minecraft.server.Main;
@@ -118,15 +120,15 @@ public static LoadedWorldData loadWorldData(
     }
 
     public void loadInitialWorlds() {
-        final var levelStemRegistry = this.server.registryAccess().lookupOrThrow(Registries.LEVEL_STEM);
-        final boolean hasWorldData = this.server.storageSource.hasWorldData();
+        final Registry<LevelStem> levelStemRegistry = this.server.registryAccess().lookupOrThrow(Registries.LEVEL_STEM);
         final LevelStem overworldStem = requireNonNull(levelStemRegistry.getValue(LevelStem.OVERWORLD), "Overworld stem missing");
+        final boolean hasWorldData = this.hasDimensionData(overworldStem);
         this.loadInitialWorld(overworldStem, hasWorldData);
         for (final LevelStem stem : levelStemRegistry) {
             if (stem == overworldStem) {
                 continue;
             }
-            this.loadInitialWorld(stem, hasWorldData);
+            this.loadInitialWorld(stem, this.hasDimensionData(stem));
         }
 
         // ((DedicatedServer) this.server).forceDifficulty();
@@ -164,6 +166,12 @@ private void loadInitialWorld(final LevelStem stem, final boolean hasWorldData)
         this.server.createLevel(stem, loading, worldDataAndGenSettings);
     }
 
+    private boolean hasDimensionData(final LevelStem stem) {
+        final ResourceKey<LevelStem> stemKey = this.server.registryAccess().lookupOrThrow(Registries.LEVEL_STEM).getResourceKey(stem).orElseThrow();
+        final ResourceKey<Level> dimensionKey = Registries.levelStemToLevel(stemKey);
+        return Files.isDirectory(this.server.storageSource.getDimensionPath(dimensionKey));
+    }
+
     public static WorldGenSettings loadWorldGenSettings(
         final LevelStorageSource.LevelStorageAccess access, final net.minecraft.core.HolderLookup.Provider registryAccess, final ResourceKey<Level> dimension
     ) {

paper-server/src/main/java/io/papermc/paper/world/migration/WorldFolderMigration.java

@@ -7,7 +7,12 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import net.minecraft.core.HolderLookup;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtAccounter;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.nbt.NbtUtils;
 import net.minecraft.resources.ResourceKey;
+import net.minecraft.util.filefix.FileFixerUpper;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.dimension.LevelStem;
 import net.minecraft.world.level.levelgen.WorldGenSettings;
@@ -91,7 +96,24 @@ private static MigrationMode classifyStartupMigration(final WorldMigrationContex
         if (!context.rootAccess().getLevelId().equals(context.worldName()) && Files.isDirectory(context.rootAccess().parent().getLevelPath(context.worldName()))) {
             return MigrationMode.LEGACY_CRAFTBUKKIT_MIGRATION;
         }
-        return hasCurrentPaperData(context.rootAccess(), context.dimensionKey()) ? MigrationMode.NO_OP : MigrationMode.VANILLA_MIGRATION;
+        if (hasCurrentPaperData(context.rootAccess(), context.dimensionKey())) {
+            return MigrationMode.NO_OP;
+        }
+        // the dimension was deleted
+        if (!Files.isDirectory(context.rootAccess().getDimensionPath(context.dimensionKey()))) {
+            try {
+                final CompoundTag rawLevelData = NbtIo.readCompressed(
+                    context.rootAccess().getLevelDirectory().dataFile(), NbtAccounter.uncompressedQuota()
+                );
+                final int dataVersion = NbtUtils.getDataVersion(rawLevelData.getCompoundOrEmpty("Data"));
+                if (dataVersion >= FileFixerUpper.FILE_FIXER_INTRODUCTION_VERSION) {
+                    return MigrationMode.NO_OP;
+                }
+            } catch (final IOException ex) {
+                throw new RuntimeException("Failed to read level data for world migration classification", ex);
+            }
+        }
+        return MigrationMode.VANILLA_MIGRATION;
     }
 
     static boolean hasCurrentPaperData(final LevelStorageSource.LevelStorageAccess rootAccess, final ResourceKey<Level> dimensionKey) {