Fix double-clicking difficulty adjust sliders not resetting the value to default correctly

- Closes https://github.com/ppy/osu/issues/31888
- Supersedes / closes https://github.com/ppy/osu/pull/32060

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

@@ -3,7 +3,6 @@
 
 using System.Linq;
 using osu.Framework.Bindables;
-using osu.Framework.Graphics;
 using osu.Framework.Localisation;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.ControlPoints;
@@ -63,13 +62,7 @@ namespace osu.Game.Rulesets.Osu.Mods
 
         private partial class ApproachRateSettingsControl : DifficultyAdjustSettingsControl
         {
-            protected override RoundedSliderBar<float> CreateSlider(BindableNumber<float> current) =>
+            protected override RoundedSliderBar<float> CreateSlider(BindableNumber<float> current) => new ApproachRateSlider();
-                new ApproachRateSlider
-                {
-                    RelativeSizeAxes = Axes.X,
-                    Current = current,
-                    KeyboardStep = 0.1f,
-                };
 
             /// <summary>
             /// A slider bar with more detailed approach rate info for its given value

osu.Game/Graphics/UserInterface/RoundedSliderBar.cs

@@ -10,6 +10,7 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Effects;
 using osu.Framework.Graphics.Shapes;
+using osu.Framework.Graphics.UserInterface;
 using osu.Framework.Input.Events;
 using osu.Game.Overlays;
 using Vector2 = osuTK.Vector2;
@@ -52,10 +53,21 @@ namespace osu.Game.Graphics.UserInterface
             }
         }
 
+        /// <summary>
+        /// The action to use to reset the value of <see cref="SliderBar{T}.Current"/> to the default.
+        /// Triggered on double click.
+        /// </summary>
+        public Action ResetToDefault { get; internal set; }
+
         public RoundedSliderBar()
         {
             Height = Nub.HEIGHT;
             RangePadding = Nub.DEFAULT_EXPANDED_SIZE / 2;
+            ResetToDefault = () =>
+            {
+                if (!Current.Disabled)
+                    Current.SetDefault();
+            };
             Children = new Drawable[]
             {
                 new Container
@@ -102,11 +114,7 @@ namespace osu.Game.Graphics.UserInterface
                         Origin = Anchor.TopCentre,
                         RelativePositionAxes = Axes.X,
                         Current = { Value = true },
-                        OnDoubleClicked = () =>
+                        OnDoubleClicked = () => ResetToDefault.Invoke(),
-                        {
-                            if (!Current.Disabled)
-                                Current.SetDefault();
-                        },
                     },
                 },
                 hoverClickSounds = new HoverClickSounds()

osu.Game/Rulesets/Mods/DifficultyAdjustSettingsControl.cs

@@ -31,12 +31,7 @@ namespace osu.Game.Rulesets.Mods
 
         protected sealed override Drawable CreateControl() => new SliderControl(sliderDisplayCurrent, CreateSlider);
 
-        protected virtual RoundedSliderBar<float> CreateSlider(BindableNumber<float> current) => new RoundedSliderBar<float>
+        protected virtual RoundedSliderBar<float> CreateSlider(BindableNumber<float> current) => new RoundedSliderBar<float>();
-        {
-            RelativeSizeAxes = Axes.X,
-            Current = current,
-            KeyboardStep = 0.1f,
-        };
 
         /// <summary>
         /// Guards against beatmap values displayed on slider bars being transferred to user override.
@@ -111,7 +106,21 @@ namespace osu.Game.Rulesets.Mods
             {
                 InternalChildren = new Drawable[]
                 {
-                    createSlider(currentNumber)
+                    createSlider(currentNumber).With(slider =>
+                    {
+                        slider.RelativeSizeAxes = Axes.X;
+                        slider.Current = currentNumber;
+                        slider.KeyboardStep = 0.1f;
+                        // this looks redundant, but isn't because of the various games this component plays
+                        // (`Current` is nullable and represents the underlying setting value,
+                        // `currentNumber` is not nullable and represents what is getting displayed,
+                        // therefore without this, double-clicking the slider would reset `currentNumber` to its bogus default of 0).
+                        slider.ResetToDefault = () =>
+                        {
+                            if (!Current.Disabled)
+                                Current.SetDefault();
+                        };
+                    })
                 };
 
                 AutoSizeAxes = Axes.Y;