Merge pull request #4496 from smoogipoo/reinstantiate-mods

Fix mods being reused for difficulty calculation

osu.Game/Rulesets/Difficulty/DifficultyCalculator.cs

@@ -37,6 +37,8 @@ namespace osu.Game.Rulesets.Difficulty
         /// <returns>A structure describing the difficulty of the beatmap.</returns>
         public DifficultyAttributes Calculate(params Mod[] mods)
         {
+            mods = mods.Select(m => m.CreateCopy()).ToArray();
+
             beatmap.Mods.Value = mods;
             IBeatmap playableBeatmap = beatmap.GetPlayableBeatmap(ruleset.RulesetInfo);
 

osu.Game/Rulesets/Mods/Mod.cs

@@ -65,5 +65,10 @@ namespace osu.Game.Rulesets.Mods
         /// </summary>
         [JsonIgnore]
         public virtual Type[] IncompatibleMods => new Type[] { };
+
+        /// <summary>
+        /// Creates a copy of this <see cref="Mod"/> initialised to a default state.
+        /// </summary>
+        public virtual Mod CreateCopy() => (Mod)Activator.CreateInstance(GetType());
     }
 }