Fix bug causing the star rating to change when Random is enabled

osu.Game.Rulesets.Osu/Mods/OsuModRandom.cs

@@ -14,7 +14,7 @@ namespace osu.Game.Rulesets.Osu.Mods
     /// <summary>
     /// Mod that randomises the positions of the <see cref="HitObject"/>s
     /// </summary>
-    public class OsuModRandom : ModRandom, IApplicableToBeatmap
+    public class OsuModRandom : ModRandom, IApplicableToBeatmapKeepStarRating
     {
         public override string Description => "It never gets boring!";
         public override bool Ranked => false;

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -32,6 +32,11 @@ namespace osu.Game.Beatmaps
 
         public readonly BeatmapMetadata Metadata;
 
+        /// <summary>
+        /// Only if this is set to true, changes made by mods that implement <see cref="IApplicableToBeatmapKeepStarRating"/> will be applied.
+        /// </summary>
+        public bool ApplyChangesToBeatmap;
+
         protected AudioManager AudioManager { get; }
 
         protected WorkingBeatmap(BeatmapInfo beatmapInfo, AudioManager audioManager)
@@ -166,10 +171,15 @@ namespace osu.Game.Beatmaps
 
                 foreach (var mod in mods.OfType<IApplicableToBeatmap>())
                 {
+                    if (mod is IApplicableToBeatmapKeepStarRating && !ApplyChangesToBeatmap)
+                        continue;
+
                     cancellationSource.Token.ThrowIfCancellationRequested();
                     mod.ApplyToBeatmap(converted);
                 }
 
+                ApplyChangesToBeatmap = false;
+
                 return converted;
             }
         }

osu.Game/Rulesets/Mods/IApplicableToBeatmapKeepStarRating.cs

@@ -0,0 +1,14 @@
+// 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.
+
+using osu.Game.Beatmaps;
+
+namespace osu.Game.Rulesets.Mods
+{
+    /// <summary>
+    /// Interface for a <see cref="Mod"/> that applies changes to a <see cref="Beatmap"/> after conversion and post-processing has completed without changing its difficulty
+    /// </summary>
+    public interface IApplicableToBeatmapKeepStarRating : IApplicableToBeatmap
+    {
+    }
+}

osu.Game/Screens/Play/Player.cs

@@ -455,6 +455,8 @@ namespace osu.Game.Screens.Play
                 rulesetInfo = Ruleset.Value ?? Beatmap.Value.BeatmapInfo.Ruleset;
                 ruleset = rulesetInfo.CreateInstance();
 
+                Beatmap.Value.ApplyChangesToBeatmap = true;
+
                 try
                 {
                     playable = Beatmap.Value.GetPlayableBeatmap(ruleset.RulesetInfo, Mods.Value);