Unpackaged Fabulous Maui app crashes at startup

[0x0309]

Steps to reproduce

1. dotnet new fabulous-mauicontrols -n MauiExample.App
2. dotnet build succeeds and the app can be run
3. Add the following properties to the fsproj
   • <WindowsPackageType Condition="$(TargetPlatformIdentifier) == 'windows'">None</WindowsPackageType>
   • <WindowsAppSdkUndockedRegFreeWinRTInitialize Condition="$(TargetPlatformIdentifier) == 'windows'">false</WindowsAppSdkUndockedRegFreeWinRTInitialize>
4. Update Main.fs (manually initialize because WindowsAppSdkUndockedRegFreeWinRTInitialize doesn't yet work out-of-the-box for F#, Can't build fsproj with WindowsPackageType=None microsoft/WindowsAppSDK#3663)

open System.Runtime.InteropServices
module private NativeMethods =
    [<DllImport("Microsoft.WindowsAppRuntime.dll", CharSet = CharSet.Unicode, ExactSpelling = true)>]
    extern int WindowsAppRuntime_EnsureIsLoaded()

[<AbstractClass; Sealed>]
type Initializer =

    static member AccessWindowsAppSDK () =
        NativeMethods.WindowsAppRuntime_EnsureIsLoaded ()
        |> ignore // safe to ignore return value


module Program =
    [<EntryPoint; STAThread>]
    let main args =
        Initializer.AccessWindowsAppSDK ()

        do FSharp.Maui.WinUICompat.Program.Main(args, typeof<MauiExample.App.WinUI.App>)
        0

5. Add a launch profile to run it unpackaged

"Run App": {
  "commandName": "Project"
}

6. Run the project with a debugger attached

Expected
The app launches as it did in step 2

Actual
An exception is thrown

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.Runtime.InteropServices.COMException (0x80004005): Unspecified error

   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)
   at WinRT.BaseActivationFactory._ActivateInstance[I]()
   at WinRT.ActivationFactory`1.ActivateInstance[I]()
   at Microsoft.UI.Xaml.Controls.XamlControlsResources..ctor()
   at System.RuntimeType.CreateInstanceOfT()
   --- End of inner exception stack trace ---
   at System.RuntimeType.CreateInstanceOfT()
   at System.Activator.CreateInstance[T]()
   at Microsoft.Maui.Platform.ResourceDictionaryExtensions.AddLibraryResources[T](ResourceDictionary resources)
   at Microsoft.Maui.Hosting.MauiAppBuilder.MauiCoreInitializer.<Initialize>g__SetupResources|0_1()
   at Microsoft.Maui.Hosting.MauiAppBuilder.MauiCoreInitializer.Initialize(IServiceProvider services)
   at Microsoft.Maui.Hosting.MauiAppBuilder.Build()
   at MauiExample.App.MauiProgram.CreateMauiApp()
   at MauiExample.App.WinUI.App.CreateMauiApp()
   at Microsoft.Maui.MauiWinUIApplication.OnLaunched(LaunchActivatedEventArgs args)
   at Microsoft.UI.Xaml.Application.Microsoft.UI.Xaml.IApplicationOverrides.OnLaunched(LaunchActivatedEventArgs args)
   at ABI.Microsoft.UI.Xaml.IApplicationOverrides.Do_Abi_OnLaunched_0(IntPtr thisPtr, IntPtr args)

OS: Windows 10

[TimLariviere]

@0x0309 Thanks for the report.
Unfortunately the FSharp.Maui.WinUICompat package is in itself more of a workaround than a proper library.
Its goal is to allow basic F# WinUI apps to run, and does not cover all cases.

Also, I don't have much knowledge of WinUI. The workaround logic was mostly done by @PureWeen. I only packaged it for simpler use with Fabulous. And F# WinUI is not really a priority given Microsoft itself doesn't plan any F# support.

If you or someone else are motivated to investigate the issue, I'll be happy to review the PR and release a new package for it.