From 6e497fbe966f99b1fe3c5e5309f91b4ab20537e3 Mon Sep 17 00:00:00 2001
From: Julien Lebosquain <julien@lebosquain.net>
Date: Thu, 26 Feb 2026 18:18:32 +0000
Subject: [PATCH] Support ExperimentalAttribute in XAML (#20765)

---
 external/XamlX                                             | 2 +-
 .../CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs      | 7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/external/XamlX b/external/XamlX
index c32d3040e5..009d481547 160000
--- a/external/XamlX
+++ b/external/XamlX
@@ -1 +1 @@
-Subproject commit c32d3040e536ae9768233ea5a445697632578bd0
+Subproject commit 009d4815470cf4bf71d1adbb633a5d81dcb2bb52
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
index 146bb5347a..ae12c9aca7 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
@@ -40,9 +40,9 @@ internal static class AvaloniaXamlDiagnosticCodes
     // Reserved 5000-9998
     public const string Obsolete = "AVLN5001";
 
-    internal static string XamlXDiagnosticCodeToAvalonia(object xamlException)
+    internal static string XamlXDiagnosticCodeToAvalonia(object codeOrException)
     {
-        return xamlException switch
+        return codeOrException switch
         {
             XamlXWellKnownDiagnosticCodes wellKnownDiagnosticCodes => wellKnownDiagnosticCodes switch
             {
@@ -50,6 +50,9 @@ internal static class AvaloniaXamlDiagnosticCodes
                 _ => throw new ArgumentOutOfRangeException()
             },
 
+            // ExperimentalAttribute reports its own code
+            string code => code,
+
             XamlDataContextException => DataContextResolvingError,
             XamlBindingsTransformException => BindingsError,
             XamlPropertyPathException => PropertyPathError,