[Bug][XAML] Using an intermediate base class for a ResourceDictionary fails to load when XamlCompilation enabled

[GalaxiaGuy]

Description

For various reasons, we are trying to use a resource dictionary ColorResources, which inherits from a base class BaseResources which inherits from ResourceDictionary.

When XAML compilation is enabled InitializeComponent throws a null reference exception. Stepping into it, it seems to be because it is trying to add a Color as a Style.

If I use VS for Mac Assembly browser, I see the following in InitializeComponent which includes a suspicious Style cast towards the end:

[GeneratedCode ("Xamarin.Forms.Build.Tasks.XamlG", "2.0.0.0")]
private void InitializeComponent ()
{
	if (ResourceLoader.get_IsEnabled ()) {
		ResourceLoadingQuery val = new ResourceLoadingQuery ();
		val.set_AssemblyName (typeof(ColorResources).GetTypeInfo ().Assembly.GetName ());
		val.set_ResourcePath ("ColorResources.xaml");
		val.set_Instance ((object)this);
		if (ResourceLoader.CanProvideContentFor ((ResourceLoadingQuery)(object)val)) {
			__InitComponentRuntime ();
			return;
		}
	}
	if (XamlLoader.get_XamlFileProvider () != null && XamlLoader.get_XamlFileProvider () (base.GetType ()) != null) {
		__InitComponentRuntime ();
		return;
	}
	Color red = Color.Red;
	ColorResources colorResources;
	VisualDiagnostics.RegisterSourceInfo ((object)(colorResources = this), new Uri ("ColorResources.xaml" + ";assembly=" + "Bug", UriKind.RelativeOrAbsolute), 2, 2);
	NameScope val2 = (NameScope)(object)new NameScope ();
	((ResourceDictionary)colorResources).Add ((Style)(object)red);
}

Steps to Reproduce

1. Create a ResourceDictionary subclass, and then a subclass of that.
2. Enable XAML compilation
3. Add something to the resource dictionary except a Style.
4. Instantiate the subclass.

Expected Behavior

An instance of the subclass.

Actual Behavior

A null reference exception.

Basic Information

• Version with issue: 5.0.0.1874
• Last known good version: Unknown

Reproduction Link

https://github.com/GalaxiaGuy/xf-bugs/tree/bug/resource-dictionary

Workaround

Disabling XAML compilation makes the problem go away. Not having an intermediate class makes the problem go away.