[X] wrap typeconverter exceptions in XPE (#5388)

- fixes #5378

Xamarin.Forms.Core/Xaml/TypeConversionExtensions.cs

@@ -114,8 +114,14 @@ namespace Xamarin.Forms.Xaml
 				var xfExtendedTypeConverter = xfTypeConverter as IExtendedTypeConverter;
 				if (xfExtendedTypeConverter != null)
 					return value = xfExtendedTypeConverter.ConvertFromInvariantString(str, serviceProvider);
-				if (xfTypeConverter != null)
-					return value = xfTypeConverter.ConvertFromInvariantString(str);
+				if (xfTypeConverter != null) {
+					try {
+						return value = xfTypeConverter.ConvertFromInvariantString(str);
+					}
+					catch (Exception e) {
+						throw new XamlParseException("Type conversion failed", serviceProvider, e);
+					}
+				}
 				var converterType = converter?.GetType();
 				if (converterType != null)
 				{

Xamarin.Forms.Xaml.UnitTests/Issues/Gh5378_1.xaml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+        xmlns="http://xamarin.com/schemas/2014/forms"
+        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+        x:Class="Xamarin.Forms.Xaml.UnitTests.Gh5378_1">
+    <Label Margin="1,2,3," />
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh5378_1.xaml.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[XamlCompilation(XamlCompilationOptions.Skip)]
+	public partial class Gh5378_1 : ContentPage
+	{
+		public Gh5378_1() => InitializeComponent();
+		public Gh5378_1(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 ReportSyntaxError([Values(false, true)]bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					Assert.Throws<XamlParseException>(() => MockCompiler.Compile(typeof(Gh5378_1)));
+				else
+					Assert.Throws<XamlParseException>(() => new Gh5378_1(useCompiledXaml));
+			}
+		}
+	}
+}

Xamarin.Forms.Xaml.UnitTests/Issues/Gh5378_2.xaml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="Xamarin.Forms.Xaml.UnitTests.Gh5378_2">
+    <Button Clicked="{Binding FooBar}" />
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh5378_2.xaml.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[XamlCompilation(XamlCompilationOptions.Skip)]
+	public partial class Gh5378_2 : ContentPage
+	{
+		public Gh5378_2()
+		{
+			InitializeComponent();
+		}
+
+		public Gh5378_2(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 ReportSyntaxError([Values(false, true)]bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					Assert.Throws<XamlParseException>(() => MockCompiler.Compile(typeof(Gh5378_2)));
+				else
+					Assert.Throws<XamlParseException>(() => new Gh5378_2(useCompiledXaml));
+			}
+		}
+	}
+}