Add support for detecting PaperMC 26.1 folder migration

src/main/java/org/mvplugins/multiverse/core/utils/compatibility/BukkitCompatibility.java

@@ -14,6 +14,8 @@
 
 /**
  * Compatibility class used to handle API changes in {@link Bukkit} class.
+ *
+ * @since 5.6
  */
 @ApiStatus.AvailableSince("5.6")
 public final class BukkitCompatibility {
@@ -26,6 +28,23 @@ public final class BukkitCompatibility {
         GET_WORLD_NAMESPACED_KEY_METHOD = Option.of(ReflectHelper.getMethod(Bukkit.class, "getWorld", NamespacedKey.class));
     }
 
+    /**
+     * Check whether the server is using the new dimension storage system introduced in PaperMC 26.1.
+     * <br />
+     * This is based of whether getLevelDirectory method exists in the server class,which is the main API change for
+     * the new dimension storage system.
+     *
+     * @return True if the server is using the new dimension storage system, else false.
+     *
+     * @since 5.6
+     */
+    @ApiStatus.AvailableSince("5.6")
+    public static boolean isUsingNewDimensionStorage() {
+        return GET_LEVEL_DIRECTORY_METHOD
+                .flatMap(method -> Option.of(ReflectHelper.invokeMethod(Bukkit.getServer(), method)))
+                .isDefined();
+    }
+
     /**
      * Gets the folder where all the worlds will be store. Before 26.1, all worlds are stored in the root directory
      * of the server, which can be obtained by {@link Server#getWorldContainer()}.
@@ -34,6 +53,8 @@ public final class BukkitCompatibility {
      * level directory, which needs to be manually parsed.
      *
      * @return The location where all the worlds folders should be, depending on server's mc version.
+     *
+     * @since 5.6
      */
     @ApiStatus.AvailableSince("5.6")
     @NotNull
@@ -55,6 +76,8 @@ public static Path getWorldFoldersDirectory() {
      *
      * @param nameOrKey Either a name or namespaced key string representation.
      * @return The world if it exists
+     *
+     * @since 5.6
      */
     @ApiStatus.AvailableSince("5.6")
     @NotNull

src/main/java/org/mvplugins/multiverse/core/world/WorldManager.java

@@ -317,8 +317,17 @@
         String worldName = options.worldName();
         if (!worldNameChecker.isValidWorldName(worldName)) {
             return worldActionResult(ImportFailureReason.INVALID_WORLDNAME, worldName);
-        } else if (options.doFolderCheck() && !worldNameChecker.isValidWorldFolder(worldName)) {
-            return worldActionResult(ImportFailureReason.WORLD_FOLDER_INVALID, worldName);
+        } else if (options.doFolderCheck()) {
+            //todo This is a duplicate of folder check in load world
+            WorldNameChecker.FolderStatus folderStatus = worldNameChecker.checkFolder(options.worldName());
+            if (!folderStatus.isLoadable()) {
+                return worldActionResult(ImportFailureReason.WORLD_FOLDER_INVALID, options.worldName());
+            }
+            if (folderStatus == WorldNameChecker.FolderStatus.REQUIRES_MIGRATION) {
+                Logging.info("World '%s' will be automatically migrated by PaperMC to the new dimension " +
+                                "location. If you face any issue with migration, please contact PaperMC support!",
+                        options.worldName());
+            }
         }
         return worldActionResult(options);
     }
@@ -480,8 +489,16 @@
             return doLoadBukkitWorld(bukkitWorld, mvWorld);
         }
 
-        if (options.doFolderCheck() && !worldNameChecker.isValidWorldFolder(mvWorld.getName())) {
-            return worldActionResult(LoadFailureReason.WORLD_FOLDER_INVALID, mvWorld.getName());
+        if (options.doFolderCheck()) {
+            WorldNameChecker.FolderStatus folderStatus = worldNameChecker.checkFolder(mvWorld.getName());
+            if (!folderStatus.isLoadable()) {
+                return worldActionResult(LoadFailureReason.WORLD_FOLDER_INVALID, mvWorld.getName());
+            }
+            if (folderStatus == WorldNameChecker.FolderStatus.REQUIRES_MIGRATION) {
+                Logging.info("World '%s' will be automatically migrated by PaperMC to the new dimension " +
+                        "location. If you face any issue with migration, please contact PaperMC support!",
+                        mvWorld.getName());
+            }
         }
 
         WorldCreator worldCreator = WorldCreator.name(mvWorld.getName())

src/main/java/org/mvplugins/multiverse/core/world/helpers/WorldNameChecker.java

@@ -5,8 +5,9 @@
 import java.util.Locale;
 import java.util.Set;
 
-import com.dumptruckman.minecraft.util.Logging;
 import io.vavr.control.Option;
+import org.bukkit.Bukkit;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jvnet.hk2.annotations.Service;
@@ -95,7 +96,7 @@
      * @return True if check result is valid, else false.
      */
     public boolean isValidWorldFolder(@Nullable String worldName) {
-        return checkFolder(worldName) == FolderStatus.VALID;
+        return checkFolder(worldName).loadable;
     }
 
     /**
@@ -105,7 +106,7 @@
      * @return True if check result is valid, else false.
      */
     public boolean isValidWorldFolder(@Nullable File worldFolder) {
-        return checkFolder(worldFolder) == FolderStatus.VALID;
+        return checkFolder(worldFolder).loadable;
     }
 
     /**
@@ -120,7 +121,13 @@
             return FolderStatus.DOES_NOT_EXIST;
         }
         File worldFolder = BukkitCompatibility.getWorldFoldersDirectory().resolve(worldName).toFile();
-        Logging.finer("Checking valid folder for world '%s' at: '%s'", worldName, worldFolder.getPath());
+        if (BukkitCompatibility.isUsingNewDimensionStorage()) {
+            File oldWorldFolder = Bukkit.getWorldContainer().toPath().resolve(worldName).toFile();
+            if (checkFolder(oldWorldFolder) == FolderStatus.VALID) {
+                return FolderStatus.REQUIRES_MIGRATION;
+            }
+        }
+
         return checkFolder(worldFolder);
     }
 
@@ -230,16 +237,39 @@
         /**
          * Folder is valid.
          */
-        VALID,
+        VALID(true),
+
+        /**
+         * This folder will cause PaperMC to migrate to new dimension world folder in 26.1+
+         */
+        REQUIRES_MIGRATION(true),
 
         /**
          * Folder exist, but contents in it doesnt look like a world.
          */
-        NOT_A_WORLD,
+        NOT_A_WORLD(false),
 
         /**
          * Folder does not exist.
          */
-        DOES_NOT_EXIST
+        DOES_NOT_EXIST(false),
+        ;
+
+        private final boolean loadable;
+
+        FolderStatus(boolean loadable) {
+            this.loadable = loadable;
+        }
+
+        /**
+         * Whether this folder status is loadable, meaning it has the basic world data and can be loaded as a world.
+         * Note that this does not guarantee the server will definitely load the world with no errors.
+         *
+         * @return True if folder probably is loadable by the server, else false.
+         */
+        @ApiStatus.AvailableSince("5.6")
+        public boolean isLoadable() {
+            return loadable;
+        }
     }
 }