Add `FindProvider` lookup function

osu.Game.Rulesets.Mania/Skinning/Legacy/ManiaLegacySkinTransformer.cs

@@ -69,10 +69,10 @@ public ManiaLegacySkinTransformer(ISkinSource source, IBeatmap beatmap)
 
         private void sourceChanged()
         {
-            isLegacySkin = new Lazy<bool>(() => Source.GetConfig<LegacySkinConfiguration.LegacySetting, decimal>(LegacySkinConfiguration.LegacySetting.Version) != null);
-            hasKeyTexture = new Lazy<bool>(() => Source.GetAnimation(
+            isLegacySkin = new Lazy<bool>(() => Source.FindProvider(s => s.GetConfig<LegacySkinConfiguration.LegacySetting, decimal>(LegacySkinConfiguration.LegacySetting.Version) != null) != null);
+            hasKeyTexture = new Lazy<bool>(() => Source.FindProvider(s => s.GetAnimation(
                 this.GetManiaSkinConfig<string>(LegacyManiaSkinConfigurationLookups.KeyImage, 0)?.Value
-                ?? "mania-key1", true, true) != null);
+                ?? "mania-key1", true, true) != null) != null);
         }
 
         public override Drawable GetDrawableComponent(ISkinComponent component)

osu.Game.Rulesets.Osu/Skinning/Legacy/OsuLegacySkinTransformer.cs

@@ -29,7 +29,7 @@ public OsuLegacySkinTransformer(ISkinSource source)
 
         private void sourceChanged()
         {
-            hasHitCircle = new Lazy<bool>(() => Source.GetTexture("hitcircle") != null);
+            hasHitCircle = new Lazy<bool>(Source.FindProvider(s => s.GetTexture("hitcircle") != null) != null);
         }
 
         public override Drawable GetDrawableComponent(ISkinComponent component)

osu.Game/Skinning/ISkin.cs

@@ -57,5 +57,13 @@ public interface ISkin
         /// <returns>A matching value boxed in an <see cref="IBindable{TValue}"/>, or null if unavailable.</returns>
         [CanBeNull]
         IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup);
+
+        /// <summary>
+        /// For the specified texture, find any potential skin that can fulfill the lookup.
+        /// This should be used for cases where subsequent lookups (for related components) need to occur on the same skin.
+        /// </summary>
+        /// <returns>The skin to be used for subsequent lookups, or <c>null</c> if none is available.</returns>
+        [CanBeNull]
+        ISkin FindProvider(Func<ISkin, bool> lookupFunction) => lookupFunction(this) ? this : null;
     }
 }

osu.Game/Skinning/LegacySkin.cs

@@ -556,5 +556,16 @@ protected override void Dispose(bool isDisposing)
             Textures?.Dispose();
             Samples?.Dispose();
         }
+
+        ISkin ISkin.FindProvider(Func<ISkin, bool> lookupFunction)
+        {
+            if (lookupFunction(this))
+                return this;
+
+            if (!fallbackToDefault)
+                return null;
+
+            return (legacyDefaultFallback as ISkin)?.FindProvider(lookupFunction);
+        }
     }
 }

osu.Game/Skinning/SkinProvidingContainer.cs

@@ -41,6 +41,14 @@ public SkinProvidingContainer(ISkin skin)
             RelativeSizeAxes = Axes.Both;
         }
 
+        public ISkin FindProvider(Func<ISkin, bool> lookupFunction)
+        {
+            if (lookupFunction(skin))
+                return skin;
+
+            return fallbackSource.FindProvider(lookupFunction);
+        }
+
         public Drawable GetDrawableComponent(ISkinComponent component)
         {
             Drawable sourceDrawable;