From 58ceab0e595671756b522013d06870b75c44051b Mon Sep 17 00:00:00 2001
From: h3xds1nz <gamingshard@protonmail.com>
Date: Sat, 22 Aug 2026 17:13:05 +0800
Subject: [PATCH] Apply changes from https://github.com/dotnet/wpf/pull/10750

Source-PR: https://github.com/dotnet/wpf/pull/10750
Source-Head-SHA: 37491a8add50bb0238c7aef6fdd030bcf29aa397
---
 .../System/Xaml/XamlMarkupExtensionWriter.cs  |  9 +++---
 .../System.Xaml/System/Xaml/XamlXmlWriter.cs  | 31 ++++---------------
 2 files changed, 10 insertions(+), 30 deletions(-)

diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlMarkupExtensionWriter.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlMarkupExtensionWriter.cs
index b44a6c9a1..c2307a628 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlMarkupExtensionWriter.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlMarkupExtensionWriter.cs
@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -129,13 +129,12 @@ void CheckMemberForUniqueness(Node objectNode, XamlMember property)
             {
                 if (objectNode.Members == null)
                 {
-                    objectNode.Members = new XamlPropertySet();
+                    objectNode.Members = new HashSet<XamlMember>() { property };
                 }
-                else if (objectNode.Members.Contains(property))
+                else if (!objectNode.Members.Add(property))
                 {
                     throw new InvalidOperationException(SR.Format(SR.XamlMarkupExtensionWriterDuplicateMember, property.Name));
                 }
-                objectNode.Members.Add(property);
             }
         }
 
@@ -188,7 +187,7 @@ public XamlMember XamlProperty
                 get;
                 set;
             }
-            public XamlPropertySet Members
+            public HashSet<XamlMember> Members
             {
                 get;
                 set;
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs
index 8d12e21be..cb059f989 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs
@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -492,26 +492,23 @@ void CheckMemberForUniqueness(XamlMember property)
             {
                 // Find the top most object frame.
                 Frame objectFrame = namespaceScopes.Peek();
-                if (objectFrame.AllocatingNodeType != XamlNodeType.StartObject &&
-                    objectFrame.AllocatingNodeType != XamlNodeType.GetObject)
+                if (objectFrame.AllocatingNodeType is not XamlNodeType.StartObject and not XamlNodeType.GetObject)
                 {
                     Frame temp = namespaceScopes.Pop();
                     objectFrame = namespaceScopes.Peek();
                     namespaceScopes.Push(temp);
                 }
 
-                Debug.Assert(objectFrame.AllocatingNodeType == XamlNodeType.StartObject ||
-                             objectFrame.AllocatingNodeType == XamlNodeType.GetObject);
+                Debug.Assert(objectFrame.AllocatingNodeType is XamlNodeType.StartObject or XamlNodeType.GetObject);
 
                 if (objectFrame.Members == null)
                 {
-                    objectFrame.Members = new XamlPropertySet();
+                    objectFrame.Members = new HashSet<XamlMember>() { property };
                 }
-                else if (objectFrame.Members.Contains(property))
+                else if (!objectFrame.Members.Add(property))
                 {
                     throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterDuplicateMember, property.Name));
                 }
-                objectFrame.Members.Add(property);
             }
         }
 
@@ -684,7 +681,7 @@ public XamlMember Member
                 set;
             }
 
-            public XamlPropertySet Members
+            public HashSet<XamlMember> Members
             {
                 get;
                 set;
@@ -2162,20 +2159,4 @@ public void Reset()
         }
     }
 
-    // need to implement our own Set class to alleviate ties to System.Core.dll
-    // HashSet<T> lives in System.Core.dll
-    internal class XamlPropertySet
-    {
-        Dictionary<XamlMember, bool> dictionary = new Dictionary<XamlMember, bool>();
-
-        public bool Contains(XamlMember member)
-        {
-            return dictionary.ContainsKey(member);
-        }
-
-        public void Add(XamlMember member)
-        {
-            dictionary.Add(member, true);
-        }
-    }
 }