Make IsValidMod adjustable

osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs

@@ -137,6 +137,22 @@ namespace osu.Game.Tests.Visual.UserInterface
             AddAssert("ensure all buttons are spread out", () => modSelect.ChildrenOfType<ModButton>().All(m => m.Mods.Length <= 1));
         }
 
+        [Test]
+        public void TestChangeIsValidChangesButtonVisibility()
+        {
+            changeRuleset(0);
+
+            AddAssert("double time visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModDoubleTime)));
+
+            AddStep("make double time invalid", () => modSelect.IsValidMod = m => !(m is OsuModDoubleTime));
+            AddAssert("double time not visible", () => modSelect.ChildrenOfType<ModButton>().All(b => !b.Mods.Any(m => m is OsuModDoubleTime)));
+            AddAssert("nightcore still visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModNightcore)));
+
+            AddStep("make double time valid again", () => modSelect.IsValidMod = m => true);
+            AddAssert("double time visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModDoubleTime)));
+            AddAssert("nightcore still visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModNightcore)));
+        }
+
         private void testSingleMod(Mod mod)
         {
             selectNext(mod);

osu.Game/Overlays/Mods/ModSelectOverlay.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
@@ -31,7 +32,6 @@ namespace osu.Game.Overlays.Mods
 {
     public class ModSelectOverlay : WaveOverlayContainer
     {
-        private readonly Func<Mod, bool> isValidMod;
         public const float HEIGHT = 510;
 
         protected readonly TriangleButton DeselectAllButton;
@@ -49,6 +49,23 @@ namespace osu.Game.Overlays.Mods
         /// </summary>
         protected virtual bool Stacked => true;
 
+        [NotNull]
+        private Func<Mod, bool> isValidMod = m => true;
+
+        /// <summary>
+        /// A function that checks whether a given mod is selectable.
+        /// </summary>
+        [NotNull]
+        public Func<Mod, bool> IsValidMod
+        {
+            get => isValidMod;
+            set
+            {
+                isValidMod = value ?? throw new ArgumentNullException(nameof(value));
+                updateAvailableMods();
+            }
+        }
+
         protected readonly FillFlowContainer<ModSection> ModSectionsContainer;
 
         protected readonly ModSettingsContainer ModSettingsContainer;
@@ -67,10 +84,8 @@ namespace osu.Game.Overlays.Mods
 
         private SampleChannel sampleOn, sampleOff;
 
-        public ModSelectOverlay(Func<Mod, bool> isValidMod = null)
+        public ModSelectOverlay()
         {
-            this.isValidMod = isValidMod ?? (m => true);
-
             Waves.FirstWaveColour = Color4Extensions.FromHex(@"19b0e2");
             Waves.SecondWaveColour = Color4Extensions.FromHex(@"2280a2");
             Waves.ThirdWaveColour = Color4Extensions.FromHex(@"005774");
@@ -351,7 +366,7 @@ namespace osu.Game.Overlays.Mods
         {
             base.LoadComplete();
 
-            availableMods.BindValueChanged(availableModsChanged, true);
+            availableMods.BindValueChanged(_ => updateAvailableMods(), true);
             SelectedMods.BindValueChanged(selectedModsChanged, true);
         }
 
@@ -406,9 +421,10 @@ namespace osu.Game.Overlays.Mods
 
         public override bool OnPressed(GlobalAction action) => false; // handled by back button
 
-        private void availableModsChanged(ValueChangedEvent<Dictionary<ModType, IReadOnlyList<Mod>>> mods)
+        private void updateAvailableMods()
         {
-            if (mods.NewValue == null) return;
+            if (availableMods?.Value == null)
+                return;
 
             foreach (var section in ModSectionsContainer.Children)
             {
@@ -417,10 +433,32 @@ namespace osu.Game.Overlays.Mods
                 if (!Stacked)
                     modEnumeration = ModUtils.FlattenMods(modEnumeration);
 
-                section.Mods = modEnumeration.Where(isValidMod);
+                section.Mods = modEnumeration.Select(getValidModOrNull).Where(m => m != null);
             }
         }
 
+        /// <summary>
+        /// Returns a valid form of a given <see cref="Mod"/> if possible, or null otherwise.
+        /// </summary>
+        /// <remarks>
+        /// This is a recursive process during which any invalid mods are culled while preserving <see cref="MultiMod"/> structures where possible.
+        /// </remarks>
+        /// <param name="mod">The <see cref="Mod"/> to check.</param>
+        /// <returns>A valid form of <paramref name="mod"/> if exists, or null otherwise.</returns>
+        [CanBeNull]
+        private Mod getValidModOrNull([NotNull] Mod mod)
+        {
+            if (!(mod is MultiMod multi))
+                return IsValidMod(mod) ? mod : null;
+
+            var validSubset = multi.Mods.Select(getValidModOrNull).Where(m => m != null).ToArray();
+
+            if (validSubset.Length == 0)
+                return null;
+
+            return validSubset.Length == 1 ? validSubset[0] : new MultiMod(validSubset);
+        }
+
         private void selectedModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
         {
             foreach (var section in ModSectionsContainer.Children)

osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs

@@ -111,7 +111,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
 
         protected override BeatmapDetailArea CreateBeatmapDetailArea() => new PlayBeatmapDetailArea();
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
+        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }

osu.Game/Screens/Select/MatchSongSelect.cs

@@ -81,7 +81,7 @@ namespace osu.Game.Screens.Select
             item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
         }
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
+        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }