Merge pull request #10503 from smoogipoo/fix-mod-combinations

Fix MultiMod difficulty calculator combinations not generating correctly

osu.Game.Tests/NonVisual/DifficultyAdjustmentModCombinationsTest.cs

@@ -94,6 +94,52 @@ namespace osu.Game.Tests.NonVisual
             Assert.IsTrue(combinations[2] is ModIncompatibleWithAofA);
         }
 
+        [Test]
+        public void TestMultiModFlattening()
+        {
+            var combinations = new TestLegacyDifficultyCalculator(new ModA(), new MultiMod(new ModB(), new ModC())).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(4, combinations.Length);
+            Assert.IsTrue(combinations[0] is ModNoMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is MultiMod);
+            Assert.IsTrue(combinations[3] is MultiMod);
+
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[0] is ModA);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[1] is ModB);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[2] is ModC);
+            Assert.IsTrue(((MultiMod)combinations[3]).Mods[0] is ModB);
+            Assert.IsTrue(((MultiMod)combinations[3]).Mods[1] is ModC);
+        }
+
+        [Test]
+        public void TestIncompatibleThroughMultiMod()
+        {
+            var combinations = new TestLegacyDifficultyCalculator(new ModA(), new MultiMod(new ModB(), new ModIncompatibleWithA())).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(3, combinations.Length);
+            Assert.IsTrue(combinations[0] is ModNoMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is MultiMod);
+
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[0] is ModB);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[1] is ModIncompatibleWithA);
+        }
+
+        [Test]
+        public void TestIncompatibleWithSameInstanceViaMultiMod()
+        {
+            var combinations = new TestLegacyDifficultyCalculator(new ModA(), new MultiMod(new ModA(), new ModB())).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(3, combinations.Length);
+            Assert.IsTrue(combinations[0] is ModNoMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is MultiMod);
+
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[0] is ModA);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[1] is ModB);
+        }
+
         private class ModA : Mod
         {
             public override string Name => nameof(ModA);
@@ -112,6 +158,13 @@ namespace osu.Game.Tests.NonVisual
             public override Type[] IncompatibleMods => new[] { typeof(ModIncompatibleWithAAndB) };
         }
 
+        private class ModC : Mod
+        {
+            public override string Name => nameof(ModC);
+            public override string Acronym => nameof(ModC);
+            public override double ScoreMultiplier => 1;
+        }
+
         private class ModIncompatibleWithA : Mod
         {
             public override string Name => $"Incompatible With {nameof(ModA)}";

osu.Game/Rulesets/Difficulty/DifficultyCalculator.cs

@@ -105,10 +105,11 @@ namespace osu.Game.Rulesets.Difficulty
         /// </summary>
         public Mod[] CreateDifficultyAdjustmentModCombinations()
         {
-            return createDifficultyAdjustmentModCombinations(Array.Empty<Mod>(), DifficultyAdjustmentMods).ToArray();
+            return createDifficultyAdjustmentModCombinations(DifficultyAdjustmentMods, Array.Empty<Mod>()).ToArray();
 
-            IEnumerable<Mod> createDifficultyAdjustmentModCombinations(IEnumerable<Mod> currentSet, Mod[] adjustmentSet, int currentSetCount = 0, int adjustmentSetStart = 0)
+            static IEnumerable<Mod> createDifficultyAdjustmentModCombinations(ReadOnlyMemory<Mod> remainingMods, IEnumerable<Mod> currentSet, int currentSetCount = 0)
             {
+                // Return the current set.
                 switch (currentSetCount)
                 {
                     case 0:
@@ -128,18 +129,43 @@ namespace osu.Game.Rulesets.Difficulty
                         break;
                 }
 
-                // Apply mods in the adjustment set recursively. Using the entire adjustment set would result in duplicate multi-mod mod
-                // combinations in further recursions, so a moving subset is used to eliminate this effect
-                for (int i = adjustmentSetStart; i < adjustmentSet.Length; i++)
+                // Apply the rest of the remaining mods recursively.
+                for (int i = 0; i < remainingMods.Length; i++)
                 {
-                    var adjustmentMod = adjustmentSet[i];
-                    if (currentSet.Any(c => c.IncompatibleMods.Any(m => m.IsInstanceOfType(adjustmentMod))))
+                    var (nextSet, nextCount) = flatten(remainingMods.Span[i]);
+
+                    // Check if any mods in the next set are incompatible with any of the current set.
+                    if (currentSet.SelectMany(m => m.IncompatibleMods).Any(c => nextSet.Any(c.IsInstanceOfType)))
                         continue;
 
-                    foreach (var combo in createDifficultyAdjustmentModCombinations(currentSet.Append(adjustmentMod), adjustmentSet, currentSetCount + 1, i + 1))
+                    // Check if any mods in the next set are the same type as the current set. Mods of the exact same type are not incompatible with themselves.
+                    if (currentSet.Any(c => nextSet.Any(n => c.GetType() == n.GetType())))
+                        continue;
+
+                    // If all's good, attach the next set to the current set and recurse further.
+                    foreach (var combo in createDifficultyAdjustmentModCombinations(remainingMods.Slice(i + 1), currentSet.Concat(nextSet), currentSetCount + nextCount))
                         yield return combo;
                 }
             }
+
+            // Flattens a mod hierarchy (through MultiMod) as an IEnumerable<Mod>
+            static (IEnumerable<Mod> set, int count) flatten(Mod mod)
+            {
+                if (!(mod is MultiMod multi))
+                    return (mod.Yield(), 1);
+
+                IEnumerable<Mod> set = Enumerable.Empty<Mod>();
+                int count = 0;
+
+                foreach (var nested in multi.Mods)
+                {
+                    var (nestedSet, nestedCount) = flatten(nested);
+                    set = set.Concat(nestedSet);
+                    count += nestedCount;
+                }
+
+                return (set, count);
+            }
         }
 
         /// <summary>