From 0fcf67d1cd6e4dbf55dddc07e3ebdb5d37222c5c Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Mon, 3 Apr 2023 19:35:22 -0400
Subject: [PATCH 1/3] Add failing test

---
 .../Xaml/ResourceDictionaryTests.cs           | 54 +++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ResourceDictionaryTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ResourceDictionaryTests.cs
index bea6bc4dc8..e73ef456af 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ResourceDictionaryTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ResourceDictionaryTests.cs
@@ -307,6 +307,60 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
                 Assert.True(buttonResources.ContainsDeferredKey("Red"));
             }
         }
+        
+        [Fact]
+        public void Should_Be_Possible_To_Redefine_Referenced_Resource_ControlTheme()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Resources>
+        <ControlTheme x:Key='{x:Type Button}' TargetType='Button' />
+    </Window.Resources>
+    <UserControl>
+        <UserControl.Resources>
+            <ControlTheme x:Key='{x:Type Button}' TargetType='Button' BasedOn='{StaticResource {x:Type Button}}' />
+        </UserControl.Resources>
+    </UserControl>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var windowResources = (ResourceDictionary)window.Resources;
+                var innerResources = (ResourceDictionary)((UserControl)window.Content!).Resources;
+
+                var winButtonTheme = Assert.IsType<ControlTheme>(windowResources[typeof(Button)]);
+                var innerButtonTheme = Assert.IsType<ControlTheme>(innerResources[typeof(Button)]);
+                Assert.Equal(winButtonTheme, innerButtonTheme.BasedOn);
+            }
+        }
+        
+        [Fact]
+        public void Should_Be_Possible_To_Redefine_Referenced_Resource()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Resources>
+        <Color x:Key='SystemAccentColor'>#aaa</Color>
+    </Window.Resources>
+    <UserControl>
+        <UserControl.Resources>
+            <StaticResource x:Key='SystemAccentColor' ResourceKey='SystemAccentColor' />
+        </UserControl.Resources>
+    </UserControl>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var windowResources = (ResourceDictionary)window.Resources;
+                var innerResources = (ResourceDictionary)((UserControl)window.Content!).Resources;
+
+                var winButtonTheme = Assert.IsType<Color>(windowResources["SystemAccentColor"]);
+                var innerButtonTheme = Assert.IsType<Color>(innerResources["SystemAccentColor"]);
+                Assert.Equal(winButtonTheme, innerButtonTheme);
+            }
+        }
 
         [Fact]
         public void Dynamically_Changing_Referenced_Resources_Works_With_DynamicResource()

From 55640f0c2bc8a49ba385f376db6bdbaf64cc795b Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Mon, 3 Apr 2023 19:35:32 -0400
Subject: [PATCH 2/3] (hack?) Fix stackoverflow

---
 .../Controls/ResourceDictionary.cs            | 26 +++++++++++++++----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/src/Avalonia.Base/Controls/ResourceDictionary.cs b/src/Avalonia.Base/Controls/ResourceDictionary.cs
index 5123803f6e..878797d9b6 100644
--- a/src/Avalonia.Base/Controls/ResourceDictionary.cs
+++ b/src/Avalonia.Base/Controls/ResourceDictionary.cs
@@ -15,6 +15,7 @@ namespace Avalonia.Controls
     /// </summary>
     public class ResourceDictionary : IResourceDictionary
     {
+        private DeferredItem? s_lastDeferredItem;
         private Dictionary<object, object?>? _inner;
         private IResourceHost? _owner;
         private AvaloniaList<IResourceProvider>? _mergedDictionaries;
@@ -241,12 +242,27 @@ namespace Avalonia.Controls
             {
                 if (value is DeferredItem deffered)
                 {
-                    _inner[key] = value = deffered.Factory(null) switch
+                    // Avoid simple reentrancy, which could commonly occur on redefining the resource.
+                    if (s_lastDeferredItem == deffered)
                     {
-                        ITemplateResult t => t.Result,
-                        object v => v,
-                        _ => null,
-                    };
+                        value = null;
+                        return false;
+                    }
+
+                    try
+                    {
+                        s_lastDeferredItem = deffered;
+                        _inner[key] = value = deffered.Factory(null) switch
+                        {
+                            ITemplateResult t => t.Result,
+                            { } v => v,
+                            _ => null,
+                        };
+                    }
+                    finally
+                    {
+                        s_lastDeferredItem = null;
+                    }
                 }
                 return true;
             }

From eb09e522c115bfae03c91e8bf7fdba03414e25ac Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Tue, 4 Apr 2023 11:48:20 -0400
Subject: [PATCH 3/3] Changes after review

---
 src/Avalonia.Base/Controls/ResourceDictionary.cs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/Avalonia.Base/Controls/ResourceDictionary.cs b/src/Avalonia.Base/Controls/ResourceDictionary.cs
index 878797d9b6..231a19baab 100644
--- a/src/Avalonia.Base/Controls/ResourceDictionary.cs
+++ b/src/Avalonia.Base/Controls/ResourceDictionary.cs
@@ -15,7 +15,7 @@ namespace Avalonia.Controls
     /// </summary>
     public class ResourceDictionary : IResourceDictionary
     {
-        private DeferredItem? s_lastDeferredItem;
+        private object? lastDeferredItemKey;
         private Dictionary<object, object?>? _inner;
         private IResourceHost? _owner;
         private AvaloniaList<IResourceProvider>? _mergedDictionaries;
@@ -243,7 +243,7 @@ namespace Avalonia.Controls
                 if (value is DeferredItem deffered)
                 {
                     // Avoid simple reentrancy, which could commonly occur on redefining the resource.
-                    if (s_lastDeferredItem == deffered)
+                    if (lastDeferredItemKey == key)
                     {
                         value = null;
                         return false;
@@ -251,7 +251,7 @@ namespace Avalonia.Controls
 
                     try
                     {
-                        s_lastDeferredItem = deffered;
+                        lastDeferredItemKey = key;
                         _inner[key] = value = deffered.Factory(null) switch
                         {
                             ITemplateResult t => t.Result,
@@ -261,7 +261,7 @@ namespace Avalonia.Controls
                     }
                     finally
                     {
-                        s_lastDeferredItem = null;
+                        lastDeferredItemKey = null;
                     }
                 }
                 return true;