Add xmldoc and remove any question of how the intitial flow is being run

osu.Game/Skinning/RulesetSkinProvidingContainer.cs

@@ -55,25 +55,15 @@ protected override IReadOnlyDependencyContainer CreateChildDependencies(IReadOnl
             if (Ruleset.CreateResourceStore() is IResourceStore<byte[]> resources)
                 rulesetResourcesSkin = new ResourceStoreBackedSkin(resources, parent.Get<GameHost>(), parent.Get<AudioManager>());
 
-            var dependencies = base.CreateChildDependencies(parent);
-
-            // ensure sources are populated and ready for use before childrens' asynchronous load flow.
-            UpdateSkinSources();
-
-            return dependencies;
+            return base.CreateChildDependencies(parent);
         }
 
         protected override void OnSourceChanged()
-        {
-            UpdateSkinSources();
-            base.OnSourceChanged();
-        }
-
-        protected virtual void UpdateSkinSources()
         {
             ResetSources();
 
-            var skinSources = new List<ISkin>();
+            // Populate a local list first so we can adjust the returned order as we go.
+            var sources = new List<ISkin>();
 
             Debug.Assert(ParentSource != null);
 
@@ -82,26 +72,26 @@ protected virtual void UpdateSkinSources()
                 switch (skin)
                 {
                     case LegacySkin legacySkin:
-                        skinSources.Add(GetLegacyRulesetTransformedSkin(legacySkin));
+                        sources.Add(GetLegacyRulesetTransformedSkin(legacySkin));
                         break;
 
                     default:
-                        skinSources.Add(skin);
+                        sources.Add(skin);
                         break;
                 }
             }
 
-            int lastDefaultSkinIndex = skinSources.IndexOf(skinSources.OfType<DefaultSkin>().LastOrDefault());
+            int lastDefaultSkinIndex = sources.IndexOf(sources.OfType<DefaultSkin>().LastOrDefault());
 
             // Ruleset resources should be given the ability to override game-wide defaults
             // This is achieved by placing them before the last instance of DefaultSkin.
             // Note that DefaultSkin may not be present in some test scenes.
             if (lastDefaultSkinIndex >= 0)
-                skinSources.Insert(lastDefaultSkinIndex, rulesetResourcesSkin);
+                sources.Insert(lastDefaultSkinIndex, rulesetResourcesSkin);
             else
-                skinSources.Add(rulesetResourcesSkin);
+                sources.Add(rulesetResourcesSkin);
 
-            foreach (var skin in skinSources)
+            foreach (var skin in sources)
                 AddSource(skin);
         }
 

osu.Game/Skinning/SkinProvidingContainer.cs

@@ -64,6 +64,10 @@ protected SkinProvidingContainer()
             RelativeSizeAxes = Axes.Both;
         }
 
+        /// <summary>
+        /// Add a new skin to this provider. Will be added to the end of the lookup order precedence.
+        /// </summary>
+        /// <param name="skin">The skin to add.</param>
         protected void AddSource(ISkin skin)
         {
             skinSources.Add(skin, new DisableableSkinSource(skin, this));
@@ -72,14 +76,22 @@ protected void AddSource(ISkin skin)
                 source.SourceChanged += anySourceChanged;
         }
 
+        /// <summary>
+        /// Remove a skin from this provider.
+        /// </summary>
+        /// <param name="skin">The skin to remove.</param>
         protected void RemoveSource(ISkin skin)
         {
-            skinSources.Remove(skin);
+            if (!skinSources.Remove(skin))
+                return;
 
             if (skin is ISkinSource source)
-                source.SourceChanged += anySourceChanged;
+                source.SourceChanged -= anySourceChanged;
         }
 
+        /// <summary>
+        /// Clears all skin sources.
+        /// </summary>
         protected void ResetSources()
         {
             foreach (var skin in AllSources.ToArray())
@@ -176,7 +188,8 @@ public IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup)
         }
 
         /// <summary>
-        /// Invoked when any source has changed (either <see cref="ParentSource"/> or <see cref="AllSources"/>
+        /// Invoked when any source has changed (either <see cref="ParentSource"/> or a source registered via <see cref="AddSource"/>).
+        /// This is also invoked once initially during <see cref="CreateChildDependencies"/> to ensure sources are ready for children consumption.
         /// </summary>
         protected virtual void OnSourceChanged() { }
 
@@ -190,6 +203,8 @@ protected override IReadOnlyDependencyContainer CreateChildDependencies(IReadOnl
 
             dependencies.CacheAs<ISkinSource>(this);
 
+            anySourceChanged();
+
             return dependencies;
         }