Paper/nms-patches/Convertable.patch

--- a/net/minecraft/server/Convertable.java
+++ b/net/minecraft/server/Convertable.java
@@ -175,8 +175,10 @@
         };
     }
 
-    public Convertable.ConversionSession c(String s) throws IOException {
-        return new Convertable.ConversionSession(s);
+    // CraftBukkit start
+    public Convertable.ConversionSession c(String s, ResourceKey<WorldDimension> dimensionType) throws IOException {
+        return new Convertable.ConversionSession(s, dimensionType);
+        // CraftBukkit end
     }
 
     public class ConversionSession implements AutoCloseable {
@@ -185,8 +187,12 @@
         public final java.nio.file.Path folder;
         private final String levelName;
         private final Map<SavedFile, java.nio.file.Path> e = Maps.newHashMap();
+        // CraftBukkit start
+        private final ResourceKey<WorldDimension> dimensionType;
 
-        public ConversionSession(String s) throws IOException {
+        public ConversionSession(String s, ResourceKey<WorldDimension> dimensionType) throws IOException {
+            this.dimensionType = dimensionType;
+            // CraftBukkit end
             this.levelName = s;
             this.folder = Convertable.this.universe.resolve(s);
             this.lock = SessionLock.a(this.folder);
@@ -203,9 +209,23 @@
         }
 
         public File a(ResourceKey<World> resourcekey) {
-            return DimensionManager.a(resourcekey, this.folder.toFile());
+            // CraftBukkit start
+            return this.getFolder(this.folder.toFile());
         }
 
+        private File getFolder(File file) {
+            if (dimensionType == WorldDimension.OVERWORLD) {
+                return file;
+            } else if (dimensionType == WorldDimension.THE_NETHER) {
+                return new File(file, "DIM-1");
+            } else if (dimensionType == WorldDimension.THE_END) {
+                return new File(file, "DIM1");
+            } else {
+                throw new IllegalArgumentException("Unknwon dimension " + this.dimensionType);
+            }
+        }
+        // CraftBukkit end
+
         private void checkSession() {
             if (!this.lock.a()) {
                 throw new IllegalStateException("Lock is no longer valid");