[C] Fix binding to interface-inherited properties like IReadOnlyList<T>.Count

src/Controls/src/Core/BindingExpression.cs

@@ -318,6 +318,28 @@ PropertyInfo GetIndexer(TypeInfo sourceType, string indexerName, string content)
 			return null;
 		}
 
+		PropertyInfo GetProperty(TypeInfo sourceType, string propertyName)
+		{
+			// First, check the type and its base classes
+			TypeInfo type = sourceType;
+			do
+			{
+				var property = type.GetDeclaredProperty(propertyName);
+				if (property != null)
+					return property;
+			} while ((type = type.BaseType?.GetTypeInfo()) != null);
+
+			// If not found, check implemented interfaces (for interface-inherited properties like IReadOnlyList<T>.Count)
+			foreach (var iface in sourceType.ImplementedInterfaces)
+			{
+				var property = GetProperty(iface.GetTypeInfo(), propertyName);
+				if (property != null)
+					return property;
+			}
+
+			return null;
+		}
+
 
 		void SetupPart(TypeInfo sourceType, BindingExpressionPart part)
 		{
@@ -382,11 +404,7 @@ void SetupPart(TypeInfo sourceType, BindingExpressionPart part)
 			}
 			else
 			{
-				TypeInfo type = sourceType;
-				do
-				{
-					property = type.GetDeclaredProperty(part.Content);
-				} while (property == null && (type = type.BaseType?.GetTypeInfo()) != null);
+				property = GetProperty(sourceType, part.Content);
 			}
 			if (property != null)
 			{

src/Controls/tests/SourceGen.UnitTests/Maui32879Tests.cs

@@ -60,6 +60,7 @@ public TestPage()
 // </auto-generated>
 //------------------------------------------------------------------------------
 #nullable enable
+#pragma warning disable CS0219 // Variable is assigned but its value is never used
 
 namespace Test;
 

src/Controls/tests/Xaml.UnitTests/Issues/Maui13872.xaml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Microsoft.Maui.Controls.Xaml.UnitTests"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Maui13872">
+    <VerticalStackLayout>
+	<Label x:Name="label0" Text="{Binding List.Count}"/>
+	<Label x:Name="label1" Text="{Binding ListCount}"/> 
+        <Label x:Name="label2" Text="{Binding List.Count}" x:DataType="local:Maui13872ViewModel"/>
+        <Label x:Name="label3" Text="{Binding ListCount}" x:DataType="local:Maui13872ViewModel"/>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui13872.xaml.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Maui13872 : ContentPage
+{
+	public Maui13872() => InitializeComponent();
+
+	[TestFixture]
+	class Tests
+	{
+		[Test]
+		public void CompiledBindingToIReadOnlyListCount([Values] XamlInflator inflator)
+		{
+			var page = new Maui13872(inflator);
+			page.BindingContext = new Maui13872ViewModel();
+
+			// Uncompiled bindings (no x:DataType) - should work with all inflators
+			Assert.That(page.label0.Text, Is.EqualTo("3"), "Uncompiled binding to List.Count");
+			Assert.That(page.label1.Text, Is.EqualTo("3"), "Uncompiled binding to ListCount");
+
+			// Compiled bindings (with x:DataType) - IReadOnlyList<T>.Count should resolve correctly.
+			// Count is defined on IReadOnlyCollection<T> which IReadOnlyList<T> inherits.
+			Assert.That(page.label2.Text, Is.EqualTo("3"), "Compiled binding to List.Count");
+			Assert.That(page.label3.Text, Is.EqualTo("3"), "Compiled binding to ListCount");
+		}
+	}
+}
+
+public class Maui13872ViewModel
+{
+	private readonly string[] _list = ["Bill", "Steve", "John"];
+
+	public IReadOnlyList<string> List => _list;
+
+	public int ListCount => _list.Length;
+}