[X] Find most derived ABP (#12085)

- fixes #12025

Xamarin.Forms.Build.Tasks/BindablePropertyReferenceExtensions.cs

@@ -26,7 +26,7 @@ namespace Xamarin.Forms.Build.Tasks
 												md.IsStatic &&
 												md.IsPublic &&
 												md.Parameters.Count == 1 &&
-												md.Parameters[0].ParameterType.InheritsFromOrImplements(module.ImportReference(("Xamarin.Forms.Core", "Xamarin.Forms", "BindableObject"))), module).SingleOrDefault()?.Item1;
+												md.Parameters[0].ParameterType.InheritsFromOrImplements(module.ImportReference(("Xamarin.Forms.Core", "Xamarin.Forms", "BindableObject"))), module).FirstOrDefault()?.Item1;
 			if (getter == null)
 				throw new BuildException(BuildExceptionCode.BPName, iXmlLineInfo, null, bpName, bpRef.DeclaringType);
 
@@ -43,7 +43,7 @@ namespace Xamarin.Forms.Build.Tasks
 												md.IsStatic &&
 												md.IsPublic &&
 												md.Parameters.Count == 1 &&
-												md.Parameters[0].ParameterType.InheritsFromOrImplements(module.ImportReference(("Xamarin.Forms.Core", "Xamarin.Forms", "BindableObject"))), module).SingleOrDefault()?.Item1;
+												md.Parameters[0].ParameterType.InheritsFromOrImplements(module.ImportReference(("Xamarin.Forms.Core", "Xamarin.Forms", "BindableObject"))), module).FirstOrDefault()?.Item1;
 
 			var attributes = new List<CustomAttribute>();
 			if (property != null && property.HasCustomAttributes)

Xamarin.Forms.Xaml.UnitTests/Issues/Gh12025.xaml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+        xmlns="http://xamarin.com/schemas/2014/forms"
+        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+        xmlns:local="using:Xamarin.Forms.Xaml.UnitTests"
+        x:Class="Xamarin.Forms.Xaml.UnitTests.Gh12025"
+        local:Gh12025NavPage.IconColor="HotPink">
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh12025.xaml.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	public class Gh12025NavPage : NavigationPage
+	{
+		public static new readonly BindableProperty IconColorProperty = BindableProperty.CreateAttached("IconColor", typeof(Color), typeof(Page), Color.Default);
+		public static void SetIconColor(Page page, Color barTintColor) => page.SetValue(IconColorProperty, barTintColor);
+		public static Color GetIconColor(Page page) => (Color)page.GetValue(IconColorProperty);
+	}
+
+	public partial class Gh12025 : ContentPage
+	{
+		public Gh12025() => InitializeComponent();
+		public Gh12025(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		[TestFixture]
+		class Tests
+		{
+			[SetUp] public void Setup() => Device.PlatformServices = new MockPlatformServices();
+			[TearDown] public void TearDown() => Device.PlatformServices = null;
+
+			[Test]
+			public void FindMostDerivedABP([Values(false, true)] bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					Assert.DoesNotThrow(() => MockCompiler.Compile(typeof(Gh12025)));
+				var layout = new Gh12025(useCompiledXaml);
+				Assert.That(NavigationPage.GetIconColor(layout), Is.EqualTo(NavigationPage.IconColorProperty.DefaultValue));
+				Assert.That(Gh12025NavPage.GetIconColor(layout), Is.EqualTo(Color.HotPink));
+			}
+		}
+	}
+}