Add debug output for skin configuration lookups

We've struggle with debugging these over the years so I think this was
worth a couple of hours of work.

Example of osu! lookups:

```log
[runtime] 2023-09-06 08:38:30 [verbose]: BeatmapSkinProvidingContainer.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacyBeatmapSkin{ Name: Vickeblanka - Lucky Ending (TV Size) (tears_) [Normal] } } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-RulesetSkinProvidingContainer.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-|-LegacySkin{ Name: Test Skin [test-skin] }.GetConfig(lookup: SpinnerFrequencyModulate) 🟢
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-|-DefaultLegacySkin{ Name: osu! "classic" (2013) }.GetConfig(lookup: SpinnerFrequencyModulate) 🟢
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: osu.Game.Skinning.ResourceStoreBackedSkin }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-osu.Game.Skinning.ResourceStoreBackedSkin.GetConfig(lookup: SpinnerFrequencyModulate) 🔴
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: TrianglesSkin{ Name: osu! "triangles" (2017) } }.GetConfig(lookup: SpinnerFrequencyModulate)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-TrianglesSkin{ Name: osu! "triangles" (2017) }.GetConfig(lookup: SpinnerFrequencyModulate) 🔴
[runtime] 2023-09-06 08:38:30 [verbose]:
[runtime] 2023-09-06 08:38:30 [verbose]: BeatmapSkinProvidingContainer.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacyBeatmapSkin{ Name: Vickeblanka - Lucky Ending (TV Size) (tears_) [Normal] } } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-RulesetSkinProvidingContainer.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-|-LegacySkin{ Name: Test Skin [test-skin] }.GetConfig(lookup: ScorePrefix) 🟢
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-|-DefaultLegacySkin{ Name: osu! "classic" (2013) }.GetConfig(lookup: ScorePrefix) 🟢
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: osu.Game.Skinning.ResourceStoreBackedSkin }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-osu.Game.Skinning.ResourceStoreBackedSkin.GetConfig(lookup: ScorePrefix) 🔴
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: TrianglesSkin{ Name: osu! "triangles" (2017) } }.GetConfig(lookup: ScorePrefix)
[runtime] 2023-09-06 08:38:30 [verbose]: |-|-|-TrianglesSkin{ Name: osu! "triangles" (2017) }.GetConfig(lookup: ScorePrefix) 🔴
```

Example of osu!mania lookups:

```log
[runtime] 2023-09-06 08:28:34 [verbose]: |-RulesetSkinProvidingContainer.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnWidth col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } } }.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnWidth col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnWidth col:0 totalcols:4])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-|-LegacySkin{ Name: Test Skin [test-skin] }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnWidth col:0 totalcols:4]) 🔴
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } } }.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnWidth col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnWidth col:0 totalcols:4])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-|-DefaultLegacySkin{ Name: osu! "classic" (2013) }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnWidth col:0 totalcols:4]) 🟢
[runtime] 2023-09-06 08:28:34 [verbose]:
[runtime] 2023-09-06 08:28:34 [verbose]: BeatmapSkinProvidingContainer.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnSpacing col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacyBeatmapSkin{ Name: antiPLUR - Runengon (Raveille) [Easy] } } }.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnSpacing col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-RulesetSkinProvidingContainer.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnSpacing col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } } }.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnSpacing col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-SkinTransformer{ Skin: LegacySkin{ Name: Test Skin [test-skin] } }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnSpacing col:0 totalcols:4])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-|-LegacySkin{ Name: Test Skin [test-skin] }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnSpacing col:0 totalcols:4]) 🔴
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-SkinProvidingContainer+DisableableSkinSource{ skin: SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } } }.GetConfig(lookup: [ManiaSkinConfigurationLookup lookup:ColumnSpacing col:0])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-SkinTransformer{ Skin: DefaultLegacySkin{ Name: osu! "classic" (2013) } }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnSpacing col:0 totalcols:4])
[runtime] 2023-09-06 08:28:34 [verbose]: |-|-|-|-DefaultLegacySkin{ Name: osu! "classic" (2013) }.GetConfig(lookup: [LegacyManiaSkinConfigurationLookup lookup:ColumnSpacing col:0 totalcols:4]) 🟢
[runtime] 2023-09-06 08:28:34 [verbose]:

```

osu.Game.Rulesets.Mania/Skinning/ManiaSkinConfigurationLookup.cs

@@ -30,5 +30,7 @@ namespace osu.Game.Rulesets.Mania.Skinning
             Lookup = lookup;
             ColumnIndex = columnIndex;
         }
+
+        public override string ToString() => $"[{nameof(ManiaSkinConfigurationLookup)} lookup:{Lookup} col:{ColumnIndex}]";
     }
 }

osu.Game/Skinning/ArgonSkin.cs

@@ -219,15 +219,20 @@ namespace osu.Game.Skinning
                     switch (global)
                     {
                         case GlobalSkinColours.ComboColours:
+                        {
+                            LogLookupDebug(this, lookup, LookupDebugType.Hit);
                             return SkinUtils.As<TValue>(new Bindable<IReadOnlyList<Color4>?>(Configuration.ComboColours));
                         }
+                    }
 
                     break;
 
                 case SkinComboColourLookup comboColour:
+                    LogLookupDebug(this, lookup, LookupDebugType.Hit);
                     return SkinUtils.As<TValue>(new Bindable<Color4>(getComboColour(Configuration, comboColour.ColourIndex)));
             }
 
+            LogLookupDebug(this, lookup, LookupDebugType.Miss);
             return null;
         }
 

osu.Game/Skinning/LegacyBeatmapSkin.cs

@@ -72,6 +72,8 @@ namespace osu.Game.Skinning
                     // If it is decided that we need this due to beatmaps somehow using it, the default (1.0 specified in LegacySkinDecoder.CreateTemplateObject)
                     // needs to be removed else it will cause incorrect skin behaviours. This is due to the config lookup having no context of which skin
                     // it should be returning the version for.
+
+                    Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Miss);
                     return null;
             }
 

osu.Game/Skinning/LegacyManiaSkinConfigurationLookup.cs

@@ -30,6 +30,8 @@ namespace osu.Game.Skinning
             Lookup = lookup;
             ColumnIndex = columnIndex;
         }
+
+        public override string ToString() => $"[{nameof(LegacyManiaSkinConfigurationLookup)} lookup:{Lookup} col:{ColumnIndex} totalcols:{TotalColumns}]";
     }
 
     public enum LegacyManiaSkinConfigurationLookups

osu.Game/Skinning/LegacySkin.cs

@@ -83,6 +83,10 @@ namespace osu.Game.Skinning
         }
 
         public override IBindable<TValue>? GetConfig<TLookup, TValue>(TLookup lookup)
+        {
+            bool wasHit = true;
+
+            try
             {
                 switch (lookup)
                 {
@@ -125,8 +129,14 @@ namespace osu.Game.Skinning
                         return genericLookup<TLookup, TValue>(lookup);
                 }
 
+                wasHit = false;
                 return null;
             }
+            finally
+            {
+                LogLookupDebug(this, lookup, wasHit ? LookupDebugType.Hit : LookupDebugType.Miss);
+            }
+        }
 
         private IBindable<TValue>? lookupForMania<TValue>(LegacyManiaSkinConfigurationLookup maniaLookup)
         {

osu.Game/Skinning/ResourceStoreBackedSkin.cs

@@ -46,7 +46,10 @@ namespace osu.Game.Skinning
         public IBindable<TValue>? GetConfig<TLookup, TValue>(TLookup lookup)
             where TLookup : notnull
             where TValue : notnull
-            => null;
+        {
+            Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Miss);
+            return null;
+        }
 
         public void Dispose()
         {

osu.Game/Skinning/Skin.cs

@@ -6,10 +6,13 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using System.Text;
+using System.Threading;
 using Newtonsoft.Json;
 using osu.Framework.Audio.Sample;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions.TypeExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Textures;
@@ -54,6 +57,8 @@ namespace osu.Game.Skinning
 
         private readonly RealmBackedResourceStore<SkinInfo>? realmBackedStorage;
 
+        public string Name { get; }
+
         /// <summary>
         /// Construct a new skin.
         /// </summary>
@@ -63,6 +68,8 @@ namespace osu.Game.Skinning
         /// <param name="configurationFilename">An optional filename to read the skin configuration from. If not provided, the configuration will be retrieved from the storage using "skin.ini".</param>
         protected Skin(SkinInfo skin, IStorageResourceProvider? resources, IResourceStore<byte[]>? storage = null, string configurationFilename = @"skin.ini")
         {
+            Name = skin.Name;
+
             if (resources != null)
             {
                 SkinInfo = skin.ToLive(resources.RealmAccess);
@@ -239,5 +246,50 @@ namespace osu.Game.Skinning
         }
 
         #endregion
+
+        public override string ToString() => $"{GetType().ReadableName()}{{ Name: {Name} }}";
+
+        private static readonly ThreadLocal<int> nested_level = new ThreadLocal<int>(() => 0);
+
+        [Conditional("SKIN_LOOKUP_DEBUG")]
+        internal static void LogLookupDebug(object callingClass, object lookup, LookupDebugType type, [CallerMemberName] string callerMethod = "")
+        {
+            string icon = string.Empty;
+            int level = nested_level.Value;
+
+            switch (type)
+            {
+                case LookupDebugType.Hit:
+                    icon = "🟢";
+                    break;
+
+                case LookupDebugType.Miss:
+                    icon = "🔴";
+                    break;
+
+                case LookupDebugType.Enter:
+                    nested_level.Value++;
+                    break;
+
+                case LookupDebugType.Exit:
+                    nested_level.Value--;
+                    if (nested_level.Value == 0)
+                        Logger.Log(string.Empty);
+                    return;
+            }
+
+            string lookupString = lookup.ToString() ?? string.Empty;
+            string callingClassString = callingClass.ToString() ?? string.Empty;
+
+            Logger.Log($"{string.Join(null, Enumerable.Repeat("|-", level))}{callingClassString}.{callerMethod}(lookup: {lookupString}) {icon}");
+        }
+
+        internal enum LookupDebugType
+        {
+            Hit,
+            Miss,
+            Enter,
+            Exit
+        }
     }
 }

osu.Game/Skinning/SkinManager.cs

@@ -261,6 +261,10 @@ namespace osu.Game.Skinning
         private T lookupWithFallback<T>(Func<ISkin, T> lookupFunction)
             where T : class
         {
+            try
+            {
+                Skin.LogLookupDebug(this, lookupFunction, Skin.LookupDebugType.Enter);
+
                 foreach (var source in AllSources)
                 {
                     if (lookupFunction(source) is T skinSourced)
@@ -269,6 +273,11 @@ namespace osu.Game.Skinning
 
                 return null;
             }
+            finally
+            {
+                Skin.LogLookupDebug(this, lookupFunction, Skin.LookupDebugType.Exit);
+            }
+        }
 
         #region IResourceStorageProvider
 

osu.Game/Skinning/SkinProvidingContainer.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Audio.Sample;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions.TypeExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Textures;
@@ -161,6 +162,10 @@ namespace osu.Game.Skinning
             where TLookup : notnull
             where TValue : notnull
         {
+            try
+            {
+                Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Enter);
+
                 foreach (var (_, lookupWrapper) in skinSources)
                 {
                     IBindable<TValue>? bindable;
@@ -173,6 +178,11 @@ namespace osu.Game.Skinning
 
                 return ParentSource?.GetConfig<TLookup, TValue>(lookup);
             }
+            finally
+            {
+                Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Exit);
+            }
+        }
 
         /// <summary>
         /// Replace the sources used for lookups in this container.
@@ -271,6 +281,10 @@ namespace osu.Game.Skinning
                 where TLookup : notnull
                 where TValue : notnull
             {
+                try
+                {
+                    Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Enter);
+
                     switch (lookup)
                     {
                         case GlobalSkinColours:
@@ -290,6 +304,13 @@ namespace osu.Game.Skinning
 
                     return null;
                 }
+                finally
+                {
+                    Skin.LogLookupDebug(this, lookup, Skin.LookupDebugType.Exit);
+                }
+            }
+
+            public override string ToString() => $"{GetType().ReadableName()}{{ skin: {skin} }}";
         }
     }
 }

osu.Game/Skinning/SkinTransformer.cs

@@ -34,6 +34,19 @@ namespace osu.Game.Skinning
 
         public virtual ISample? GetSample(ISampleInfo sampleInfo) => Skin.GetSample(sampleInfo);
 
-        public virtual IBindable<TValue>? GetConfig<TLookup, TValue>(TLookup lookup) where TLookup : notnull where TValue : notnull => Skin.GetConfig<TLookup, TValue>(lookup);
+        public virtual IBindable<TValue>? GetConfig<TLookup, TValue>(TLookup lookup) where TLookup : notnull where TValue : notnull
+        {
+            try
+            {
+                Skinning.Skin.LogLookupDebug(this, lookup, Skinning.Skin.LookupDebugType.Enter);
+                return Skin.GetConfig<TLookup, TValue>(lookup);
+            }
+            finally
+            {
+                Skinning.Skin.LogLookupDebug(this, lookup, Skinning.Skin.LookupDebugType.Exit);
+            }
+        }
+
+        public override string ToString() => $"{nameof(SkinTransformer)}{{ Skin: {Skin} }}";
     }
 }

osu.Game/Skinning/TrianglesSkin.cs

@@ -190,15 +190,20 @@ namespace osu.Game.Skinning
                     switch (global)
                     {
                         case GlobalSkinColours.ComboColours:
+                        {
+                            LogLookupDebug(this, lookup, LookupDebugType.Hit);
                             return SkinUtils.As<TValue>(new Bindable<IReadOnlyList<Color4>?>(Configuration.ComboColours));
                         }
+                    }
 
                     break;
 
                 case SkinComboColourLookup comboColour:
+                    LogLookupDebug(this, lookup, LookupDebugType.Hit);
                     return SkinUtils.As<TValue>(new Bindable<Color4>(getComboColour(Configuration, comboColour.ColourIndex)));
             }
 
+            LogLookupDebug(this, lookup, LookupDebugType.Miss);
             return null;
         }