Fix beatmap skin properties not copying

osu.Game/Beatmaps/BeatmapManager.cs

@@ -144,7 +144,7 @@ namespace osu.Game.Beatmaps
             targetBeatmapSet.Beatmaps.Add(newBeatmapInfo);
             newBeatmapInfo.BeatmapSet = targetBeatmapSet;
 
-            beatmapModelManager.Save(newBeatmapInfo, newBeatmap);
+            beatmapModelManager.Save(newBeatmapInfo, newBeatmap, creationParameters.ReferenceBeatmapSkin);
 
             workingBeatmapCache.Invalidate(targetBeatmapSet);
             return GetWorkingBeatmap(newBeatmap.BeatmapInfo);

osu.Game/Screens/Edit/Editor.cs

@@ -9,6 +9,7 @@ using JetBrains.Annotations;
 using osu.Framework;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Shapes;
@@ -853,13 +854,14 @@ namespace osu.Game.Screens.Edit
 
         private void switchToNewDifficulty(RulesetInfo rulesetInfo, bool clearAllObjects)
             => loader?.ScheduleSwitchToNewDifficulty(new NewDifficultyCreationParameters
-            {
+            (
-                BeatmapSet = editorBeatmap.BeatmapInfo.BeatmapSet,
+                editorBeatmap.BeatmapInfo.BeatmapSet.AsNonNull(),
-                Ruleset = rulesetInfo,
+                rulesetInfo,
-                ReferenceBeatmap = playableBeatmap,
+                playableBeatmap,
-                ClearAllObjects = clearAllObjects,
+                editorBeatmap.BeatmapSkin,
-                EditorState = GetState()
+                clearAllObjects,
-            });
+                GetState()
+            ));
 
         private EditorMenuItem createDifficultySwitchMenu()
         {

osu.Game/Screens/Edit/NewDifficultyCreationParameters.cs

@@ -1,8 +1,11 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+#nullable enable
+
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets;
+using osu.Game.Skinning;
 
 namespace osu.Game.Screens.Edit
 {
@@ -11,26 +14,47 @@ namespace osu.Game.Screens.Edit
         /// <summary>
         /// The <see cref="BeatmapSetInfo"/> that should contain the newly-created difficulty.
         /// </summary>
-        public BeatmapSetInfo BeatmapSet { get; set; }
+        public BeatmapSetInfo BeatmapSet { get; }
 
         /// <summary>
         /// The <see cref="RulesetInfo"/> that the new difficulty should be playable for.
         /// </summary>
-        public RulesetInfo Ruleset { get; set; }
+        public RulesetInfo Ruleset { get; }
 
         /// <summary>
         /// A reference <see cref="IBeatmap"/> upon which the new difficulty should be based.
         /// </summary>
-        public IBeatmap ReferenceBeatmap { get; set; }
+        public IBeatmap ReferenceBeatmap { get; }
+
+        /// <summary>
+        /// A reference <see cref="ISkin"/> that the new difficulty should base its own skin upon.
+        /// </summary>
+        public ISkin? ReferenceBeatmapSkin { get; }
 
         /// <summary>
         /// Whether all objects should be cleared from the new difficulty.
         /// </summary>
-        public bool ClearAllObjects { get; set; }
+        public bool ClearAllObjects { get; }
 
         /// <summary>
         /// The saved state of the previous <see cref="Editor"/> which should be restored upon opening the newly-created difficulty.
         /// </summary>
-        public EditorState EditorState { get; set; }
+        public EditorState EditorState { get; }
+
+        public NewDifficultyCreationParameters(
+            BeatmapSetInfo beatmapSet,
+            RulesetInfo ruleset,
+            IBeatmap referenceBeatmap,
+            ISkin? referenceBeatmapSkin,
+            bool clearAllObjects,
+            EditorState editorState)
+        {
+            BeatmapSet = beatmapSet;
+            Ruleset = ruleset;
+            ReferenceBeatmap = referenceBeatmap;
+            ReferenceBeatmapSkin = referenceBeatmapSkin;
+            ClearAllObjects = clearAllObjects;
+            EditorState = editorState;
+        }
     }
 }