Add a list of mods to Skill class

Although this isn't necessary for existing official rulesets and calculators, custom calculators can have use cases for accessing mods in difficulty calculation.
For example, accounting for the effects of visual mods.

osu.Game.Rulesets.Catch/Difficulty/CatchDifficultyCalculator.cs

@@ -69,7 +69,7 @@ namespace osu.Game.Rulesets.Catch.Difficulty
             }
         }
 
-        protected override Skill[] CreateSkills(IBeatmap beatmap)
+        protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods)
         {
             halfCatcherWidth = Catcher.CalculateCatchWidth(beatmap.BeatmapInfo.BaseDifficulty) * 0.5f;
 
@@ -78,7 +78,7 @@ namespace osu.Game.Rulesets.Catch.Difficulty
 
             return new Skill[]
             {
-                new Movement(halfCatcherWidth),
+                new Movement(mods, halfCatcherWidth),
             };
         }
 

osu.Game.Rulesets.Catch/Difficulty/Skills/Movement.cs

@@ -5,6 +5,7 @@ using System;
 using osu.Game.Rulesets.Catch.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
+using osu.Game.Rulesets.Mods;
 
 namespace osu.Game.Rulesets.Catch.Difficulty.Skills
 {
@@ -25,7 +26,8 @@ namespace osu.Game.Rulesets.Catch.Difficulty.Skills
         private float lastDistanceMoved;
         private double lastStrainTime;
 
-        public Movement(float halfCatcherWidth)
+        public Movement(Mod[] mods, float halfCatcherWidth)
+            : base(mods)
         {
             HalfCatcherWidth = halfCatcherWidth;
         }

osu.Game.Rulesets.Mania/Difficulty/ManiaDifficultyCalculator.cs

@@ -68,9 +68,9 @@ namespace osu.Game.Rulesets.Mania.Difficulty
         // Sorting is done in CreateDifficultyHitObjects, since the full list of hitobjects is required.
         protected override IEnumerable<DifficultyHitObject> SortObjects(IEnumerable<DifficultyHitObject> input) => input;
 
-        protected override Skill[] CreateSkills(IBeatmap beatmap) => new Skill[]
+        protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods) => new Skill[]
         {
-            new Strain(((ManiaBeatmap)beatmap).TotalColumns)
+            new Strain(mods, ((ManiaBeatmap)beatmap).TotalColumns)
         };
 
         protected override Mod[] DifficultyAdjustmentMods

osu.Game.Rulesets.Mania/Difficulty/Skills/Strain.cs

@@ -6,6 +6,7 @@ using osu.Framework.Utils;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
 using osu.Game.Rulesets.Mania.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Objects;
 
 namespace osu.Game.Rulesets.Mania.Difficulty.Skills
@@ -24,7 +25,8 @@ namespace osu.Game.Rulesets.Mania.Difficulty.Skills
         private double individualStrain;
         private double overallStrain;
 
-        public Strain(int totalColumns)
+        public Strain(Mod[] mods, int totalColumns)
+            : base(mods)
         {
             holdEndTimes = new double[totalColumns];
             individualStrains = new double[totalColumns];

osu.Game.Rulesets.Osu/Difficulty/OsuDifficultyCalculator.cs

@@ -79,10 +79,10 @@ namespace osu.Game.Rulesets.Osu.Difficulty
             }
         }
 
-        protected override Skill[] CreateSkills(IBeatmap beatmap) => new Skill[]
+        protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods) => new Skill[]
         {
-            new Aim(),
+            new Aim(mods),
-            new Speed()
+            new Speed(mods)
         };
 
         protected override Mod[] DifficultyAdjustmentMods => new Mod[]

osu.Game.Rulesets.Osu/Difficulty/Skills/Aim.cs

@@ -4,6 +4,7 @@
 using System;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Osu.Objects;
 
@@ -17,6 +18,11 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Skills
         private const double angle_bonus_begin = Math.PI / 3;
         private const double timing_threshold = 107;
 
+        public Aim(Mod[] mods)
+            : base(mods)
+        {
+        }
+
         protected override double SkillMultiplier => 26.25;
         protected override double StrainDecayBase => 0.15;
 

osu.Game.Rulesets.Osu/Difficulty/Skills/Speed.cs

@@ -4,6 +4,7 @@
 using System;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Osu.Objects;
 
@@ -27,6 +28,11 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Skills
         private const double max_speed_bonus = 45; // ~330BPM
         private const double speed_balancing_factor = 40;
 
+        public Speed(Mod[] mods)
+            : base(mods)
+        {
+        }
+
         protected override double StrainValueOf(DifficultyHitObject current)
         {
             if (current.BaseObject is Spinner)

osu.Game.Rulesets.Taiko/Difficulty/Skills/Colour.cs

@@ -5,6 +5,7 @@ using System;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
 using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Taiko.Objects;
 
@@ -39,6 +40,11 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
         /// </summary>
         private int currentMonoLength;
 
+        public Colour(Mod[] mods)
+            : base(mods)
+        {
+        }
+
         protected override double StrainValueOf(DifficultyHitObject current)
         {
             // changing from/to a drum roll or a swell does not constitute a colour change.

osu.Game.Rulesets.Taiko/Difficulty/Skills/Rhythm.cs

@@ -5,6 +5,7 @@ using System;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
 using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Taiko.Objects;
 
@@ -47,6 +48,11 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
         /// </summary>
         private int notesSinceRhythmChange;
 
+        public Rhythm(Mod[] mods)
+            : base(mods)
+        {
+        }
+
         protected override double StrainValueOf(DifficultyHitObject current)
         {
             // drum rolls and swells are exempt.

osu.Game.Rulesets.Taiko/Difficulty/Skills/Stamina.cs

@@ -5,6 +5,7 @@ using System.Linq;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
 using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Taiko.Objects;
 
@@ -48,8 +49,10 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
         /// <summary>
         /// Creates a <see cref="Stamina"/> skill.
         /// </summary>
+        /// <param name="mods">Mods for use in skill calculations.</param>
         /// <param name="rightHand">Whether this instance is performing calculations for the right hand.</param>
-        public Stamina(bool rightHand)
+        public Stamina(Mod[] mods, bool rightHand)
+            : base(mods)
         {
             hand = rightHand ? 1 : 0;
         }

osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs

@@ -29,12 +29,12 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         {
         }
 
-        protected override Skill[] CreateSkills(IBeatmap beatmap) => new Skill[]
+        protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods) => new Skill[]
         {
-            new Colour(),
+            new Colour(mods),
-            new Rhythm(),
+            new Rhythm(mods),
-            new Stamina(true),
+            new Stamina(mods, true),
-            new Stamina(false),
+            new Stamina(mods, false),
         };
 
         protected override Mod[] DifficultyAdjustmentMods => new Mod[]

osu.Game.Tests/NonVisual/DifficultyAdjustmentModCombinationsTest.cs

@@ -212,7 +212,7 @@ namespace osu.Game.Tests.NonVisual
                 throw new NotImplementedException();
             }
 
-            protected override Skill[] CreateSkills(IBeatmap beatmap)
+            protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods)
             {
                 throw new NotImplementedException();
             }

osu.Game/Rulesets/Difficulty/DifficultyCalculator.cs

@@ -64,7 +64,7 @@ namespace osu.Game.Rulesets.Difficulty
 
         private DifficultyAttributes calculate(IBeatmap beatmap, Mod[] mods, double clockRate)
         {
-            var skills = CreateSkills(beatmap);
+            var skills = CreateSkills(beatmap, mods);
 
             if (!beatmap.HitObjects.Any())
                 return CreateDifficultyAttributes(beatmap, mods, skills, clockRate);
@@ -202,7 +202,8 @@ namespace osu.Game.Rulesets.Difficulty
         /// Creates the <see cref="Skill"/>s to calculate the difficulty of an <see cref="IBeatmap"/>.
         /// </summary>
         /// <param name="beatmap">The <see cref="IBeatmap"/> whose difficulty will be calculated.</param>
+        /// <param name="mods">Mods to calculate difficulty with.</param>
         /// <returns>The <see cref="Skill"/>s.</returns>
-        protected abstract Skill[] CreateSkills(IBeatmap beatmap);
+        protected abstract Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods);
     }
 }

osu.Game/Rulesets/Difficulty/Skills/Skill.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Mods;
 
 namespace osu.Game.Rulesets.Difficulty.Skills
 {
@@ -46,10 +47,22 @@ namespace osu.Game.Rulesets.Difficulty.Skills
         /// </summary>
         protected double CurrentStrain { get; private set; } = 1;
 
+        /// <summary>
+        /// Mods for use in skill calculations.
+        /// </summary>
+        protected IReadOnlyList<Mod> Mods => mods;
+
         private double currentSectionPeak = 1; // We also keep track of the peak strain level in the current section.
 
         private readonly List<double> strainPeaks = new List<double>();
 
+        private readonly Mod[] mods;
+
+        protected Skill(Mod[] mods)
+        {
+            this.mods = mods;
+        }
+
         /// <summary>
         /// Process a <see cref="DifficultyHitObject"/> and update current strain values accordingly.
         /// </summary>