fix: Swallow Style setter exceptions as in WinUI

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_Style.cs

@@ -8,28 +8,43 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Private.Infrastructure;
 using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Data;
 
 namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml
 {
+	// The attribute is required when running WinUI. See:
+	// https://github.com/microsoft/microsoft-ui-xaml/issues/4723#issuecomment-812753123
+	[Bindable]
+	public sealed partial class ThrowingElement : FrameworkElement
+	{
+		public ThrowingElement() => throw new Exception("Inner exception");
+	}
+
 	[TestClass]
 	public class Given_Style
 	{
-#if !WINAPPSDK // Control template does not support lambda parameter
 		[TestMethod]
 		[RunsOnUIThread]
 		public void When_StyleFailsToApply()
 		{
+			var controlTemplate = (ControlTemplate)XamlReader.Load("""
+				<ControlTemplate xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+								 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+								 xmlns:local="using:Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml">
+					<local:ThrowingElement />
+				</ControlTemplate>
+				""");
+
 			var style = new Style()
 			{
 				Setters =
 				{
-					new Setter(ContentControl.TemplateProperty, new ControlTemplate(() => throw new Exception("Inner exception")))
+					new Setter(ContentControl.TemplateProperty, controlTemplate)
 				}
 			};
 
-			var e = Assert.ThrowsException<Exception>(() => new ContentControl() { Style = style });
-			Assert.AreEqual("Inner exception", e.Message);
+			// This shouldn't throw.
+			_ = new ContentControl() { Style = style };
 		}
-#endif
 	}
 }

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_Flyout.cs

@@ -1582,8 +1582,11 @@ public async Task When_Unbound_FullFlyout()
 							new Setter(FlyoutPresenter.BorderThicknessProperty, new Thickness(0)),
 
 							// remove limit from default style
-							new Setter(FlyoutPresenter.MaxWidthProperty, double.PositiveInfinity),
-							new Setter(FlyoutPresenter.MaxHeightProperty, double.PositiveInfinity),
+							// Note that NaN isn't allowed to be set for MaxWidth and MaxHeight. However,
+							// WinUI swallows failure HResults specifically when applying style setters.
+							// So, Uno catches the exception as well.
+							new Setter(FlyoutPresenter.MaxWidthProperty, double.NaN),
+							new Setter(FlyoutPresenter.MaxHeightProperty, double.NaN),
 
 							// full stretch
 							new Setter(FlyoutPresenter.HorizontalAlignmentProperty, HorizontalAlignment.Stretch),

src/Uno.UI/UI/Xaml/Style/Style.cs

@@ -84,7 +84,30 @@ internal void ApplyTo(DependencyObject o, DependencyPropertyValuePrecedences pre
 				{
 					for (var i = 0; i < _flattenedSetters.Length; i++)
 					{
-						_flattenedSetters[i].ApplyTo(o);
+						try
+						{
+							_flattenedSetters[i].ApplyTo(o);
+						}
+						catch (Exception)
+						{
+							if (this.Log().IsEnabled(LogLevel.Warning))
+							{
+								this.Log().LogWarning($"An exception occurred while applying style setter.");
+							}
+
+							// Ideally, this should be an empty catch, keeping parity equivalent to WinUI's IGNOREHR in https://github.com/microsoft/microsoft-ui-xaml/blob/93742a178db8f625ba9299f62c21f656e0b195ad/dxaml/xcp/core/core/elements/framework.cpp#L790
+							// However, Later when default style is applied (using ImplicitStyle precedence), we don't observe that value in WinUI.
+							// As a workaround, we force-set the current value to Local precedence.
+							// Note: This workaround can be removed as long as When_Unbound_FullFlyout is passing.
+							// Maybe we are applying default styles later than we should?
+							// For now, this is very uncommon code path for already bad code that throws.
+							if (_flattenedSetters[i] is Setter { Property: { } dp })
+							{
+								var value = o.GetValue(dp);
+								this.Log().LogWarning($"Force-setting local value to '{value}'.");
+								o.SetValue(dp, value);
+							}
+						}
 					}
 				}