From e62e718a06f554cbbe1b444a832b45f4959b61f2 Mon Sep 17 00:00:00 2001
From: Tom Edwards <109803929+TomEdwardsEnscape@users.noreply.github.com>
Date: Mon, 13 Oct 2025 13:10:04 +0200
Subject: [PATCH] Fixed ExpressionParseException being reported as an internal
 compiler error (#19817)

---
 .../AvaloniaXamlIlBindingPathParser.cs        | 21 +++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathParser.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathParser.cs
index 62e81f44d8..71cc252182 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathParser.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathParser.cs
@@ -2,8 +2,10 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using Avalonia.Data.Core;
 using Avalonia.Markup.Parsers;
 using Avalonia.Utilities;
+using XamlX;
 using XamlX.Ast;
 using XamlX.Transform;
 using XamlX.Transform.Transformers;
@@ -22,8 +24,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
                 if (binding.Arguments.Count > 0 && binding.Arguments[0] is XamlAstTextNode bindingPathText)
                 {
-                    var reader = new CharacterReader(bindingPathText.Text.AsSpan());
-                    var (nodes, _) = BindingExpressionGrammar.Parse(ref reader);
+                    var nodes = GetBindingPath(bindingPathText);
 
                     if (convertedNode != null)
                     {
@@ -48,8 +49,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
                     if (bindingPathAssignment != null && bindingPathAssignment.Values[0] is XamlAstTextNode pathValue)
                     {
-                        var reader = new CharacterReader(pathValue.Text.AsSpan());
-                        var (nodes, _) = BindingExpressionGrammar.Parse(ref reader);
+                        var nodes = GetBindingPath(pathValue);
 
                         if (nodes.Count == 1 && nodes[0] is BindingExpressionGrammar.EmptyExpressionNode)
                         {
@@ -79,6 +79,19 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             return node;
         }
 
+        private static List<BindingExpressionGrammar.INode> GetBindingPath(XamlAstTextNode node)
+        {
+            try
+            {
+                var reader = new CharacterReader(node.Text.AsSpan());
+                return BindingExpressionGrammar.Parse(ref reader).Nodes;
+            }
+            catch (ExpressionParseException ex)
+            {
+                throw new XamlTransformException($"Failed to parse binding path '{node.Text}': {ex.Message}", node, ex);
+            }
+        }
+
         private static BindingExpressionGrammar.INode? ConvertLongFormPropertiesToBindingExpressionNode(
             AstTransformationContext context,
             XamlAstObjectNode binding)