File folder = new File(this.getWorldContainer(), name);
World world = this.getWorld(name);
- if (world != null) {
- return world;
+ // Paper start
+ World worldByKey = this.getWorld(creator.key());
+ if (world != null || worldByKey != null) {
+ if (world == worldByKey) {
+ return world;
+ }
+ throw new IllegalArgumentException("Cannot create a world with key " + creator.key() + " and name " + name + " one (or both) already match a world that exists");
- worldKey = ResourceKey.create(Registries.DIMENSION, new ResourceLocation(name.toLowerCase(java.util.Locale.ENGLISH)));
+ worldKey = ResourceKey.create(Registries.DIMENSION, new net.minecraft.resources.ResourceLocation(creator.key().getNamespace().toLowerCase(java.util.Locale.ENGLISH), creator.key().getKey().toLowerCase(java.util.Locale.ENGLISH))); // Paper