add fix for StackOverflow in resource loading.

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResourceInclude.cs

@@ -12,7 +12,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
     public class ResourceInclude : IResourceProvider
     {
         private Uri? _baseUri;
-        private IResourceDictionary? _loaded;        
+        private IResourceDictionary? _loaded;
+        private bool _isLoading;
 
         /// <summary>
         /// Gets the loaded resource dictionary.
@@ -22,9 +23,11 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             get
             {
                 if (_loaded is null)
-                {                    
+                {
+                    _isLoading = true;
                     var loader = new AvaloniaXamlLoader();
                     _loaded = (IResourceDictionary)loader.Load(Source, _baseUri);
+                    _isLoading = false;
                 }
 
                 return _loaded;
@@ -48,7 +51,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         bool IResourceNode.TryGetResource(object key, out object? value)
         {
-            return Loaded.TryGetResource(key, out value);
+            if(!_isLoading)
+            {
+                return Loaded.TryGetResource(key, out value);                
+            }
+
+            value = null;
+            return false;
         }
 
         void IResourceProvider.AddOwner(IResourceHost owner) => Loaded.AddOwner(owner);

src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs

@@ -13,7 +13,8 @@ namespace Avalonia.Markup.Xaml.Styling
     public class StyleInclude : IStyle, IResourceProvider
     {
         private readonly Uri _baseUri;
-        private IStyle[]? _loaded;        
+        private IStyle[]? _loaded;
+        private bool _isLoading;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StyleInclude"/> class.
@@ -49,9 +50,11 @@ namespace Avalonia.Markup.Xaml.Styling
             {
                 if (_loaded is null)
                 {
+                    _isLoading = true;
                     var loader = new AvaloniaXamlLoader();
                     var loaded = (IStyle)loader.Load(Source, _baseUri);
                     _loaded = new[] { loaded };
+                    _isLoading = false;
                 }
 
                 return _loaded?[0]!;
@@ -84,7 +87,7 @@ namespace Avalonia.Markup.Xaml.Styling
 
         public bool TryGetResource(object key, out object? value)
         {
-            if (Loaded is IResourceProvider p)
+            if (!_isLoading && Loaded is IResourceProvider p)
             {
                 return p.TryGetResource(key, out value);
             }