Allow WorldCreator to pass custom environment key

Author: Doc94

paper-api/src/main/java/org/bukkit/WorldCreator.java

@@ -15,10 +15,11 @@
  * Represents various types of options that may be used to create a world.
  */
 public class WorldCreator {
-    private final NamespacedKey key; // Paper
+    private final NamespacedKey key;
     private final String name;
     private long seed;
     private World.Environment environment = World.Environment.NORMAL;
+    private @Nullable NamespacedKey customEnvironmentKey = null;
     private ChunkGenerator generator = null;
     private BiomeProvider biomeProvider = null;
     private WorldType type = WorldType.NORMAL;
@@ -173,6 +174,7 @@ public WorldCreator copy(@NotNull WorldCreator creator) {
 
         seed = creator.seed();
         environment = creator.environment();
+        customEnvironmentKey = creator.customEnvironmentKey();
         generator = creator.generator();
         biomeProvider = creator.biomeProvider();
         type = creator.type();
@@ -243,6 +245,30 @@ public WorldCreator environment(@NotNull World.Environment env) {
         return this;
     }
 
+    /**
+     * Gets the environment key that will be used to create or load the world
+     * if {@link #environment()} is {@link World.Environment#CUSTOM CUSTOM}.
+     *
+     * @return World environment key
+     */
+    public @Nullable NamespacedKey customEnvironmentKey() {
+        return this.customEnvironmentKey;
+    }
+
+    /**
+     * Sets the environment key that will be used to create or load the world and
+     * set the environment to {@link World.Environment#CUSTOM CUSTOM}.
+     *
+     * @param customEnvironmentKey World environment key
+     * @return This object, for chaining
+     */
+    public @NotNull WorldCreator customEnvironmentKey(@Nullable NamespacedKey customEnvironmentKey) {
+        this.environment = World.Environment.CUSTOM;
+        this.customEnvironmentKey = customEnvironmentKey;
+
+        return this;
+    }
+
     /**
      * Gets the type of the world that will be created or loaded
      *

paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -1195,12 +1195,23 @@ public World createWorld(WorldCreator creator) {
             biomeProvider = this.getBiomeProvider(name);
         }
 
-        ResourceKey<LevelStem> actualDimension = switch (creator.environment()) {
-            case NORMAL -> LevelStem.OVERWORLD;
-            case NETHER -> LevelStem.NETHER;
-            case THE_END -> LevelStem.END;
-            default -> throw new IllegalArgumentException("Illegal dimension (" + creator.environment() + ")");
-        };
+        if (creator.environment() == Environment.CUSTOM && creator.customEnvironmentKey() == null) {
+            throw new IllegalArgumentException("Custom worlds must have a custom environment key");
+        }
+
+        ResourceKey<LevelStem> actualDimension;
+        if (creator.environment() == Environment.NORMAL) {
+            actualDimension = LevelStem.OVERWORLD;
+        } else if (creator.environment() == Environment.NETHER) {
+            actualDimension = LevelStem.NETHER;
+        } else if (creator.environment() == Environment.THE_END) {
+            actualDimension = LevelStem.END;
+        } else {
+            if (creator.customEnvironmentKey() == null) {
+                throw new IllegalArgumentException("Custom worlds must have a custom environment key");
+            }
+            actualDimension = CraftNamespacedKey.toResourceKey(Registries.LEVEL_STEM, creator.customEnvironmentKey());
+        }
 
         final ResourceKey<net.minecraft.world.level.Level> dimensionKey = PaperWorldLoader.dimensionKey(creator.key());
         WorldLoader.DataLoadContext context = this.console.worldLoaderContext;