Marshalling `IEnumerable<T>` in modern UWP fails

[devsko]

Describe the bug
Calling WinRT with parameters of type IEnumerable<T> in modern UWP fails with various exceptions depending on T and parameter type.

To Reproduce

1. Create a new .NET 9 UWP project
2. Add <WindowsSDKPackageVersion>10.0.26100.54</WindowsSDKPackageVersion> and <AllowUnsafeBlocks>true</AllowUnsafeBlocks> to .csproj
3. Add a Page_Loaded handler to MainPage with this code:

            new Geopath([new BasicGeoposition(0, 0, 0)]); // BasicGeoposition is a value type
            // System.InvalidCastException: Specified cast is not valid.
            //    at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForABI(Object obj, Guid iid)
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForMarshaling(Object obj, Guid iid)
            //    at WinRT.MarshalInspectable`1.CreateMarshaler2(T o, Guid iid, Boolean unwrapObject)
            //    at WinRT.MarshalInterface`1.CreateMarshaler2(T value, Guid iid)
            //    at Windows.Devices.Geolocation.Geopath._IGeopathFactoryMethods.Create(IObjectReference _obj, IEnumerable`1 positions)
            //    at Windows.Devices.Geolocation.Geopath..ctor(IEnumerable`1 positions)

            new Geopath(new BasicGeoposition[] { new(0, 0, 0) });
            // System.NotSupportedException: Cannot provide IReferenceArray`1 support for element type 'Windows.Devices.Geolocation.BasicGeoposition'.
            //    at WinRT.ComWrappersSupport.ProvideIReferenceArray(Type arrayType)
            //    at WinRT.ComWrappersSupport.GetInterfaceTableEntries(Type type)
            //    at WinRT.DefaultComWrappers.<>c.<ComputeVtables>b__7_0(Type type)
            //    at System.Runtime.CompilerServices.ConditionalWeakTable`2.GetValueLocked(TKey key, CreateValueCallback createValueCallback)
            //    at System.Runtime.CompilerServices.ConditionalWeakTable`2.GetValue(TKey key, CreateValueCallback createValueCallback)
            //    at WinRT.DefaultComWrappers.ComputeVtables(Object obj, CreateComInterfaceFlags flags, Int32& count)
            //    at System.Runtime.InteropServices.ComWrappers.TryGetOrCreateComInterfaceForObjectInternal(ObjectHandleOnStack comWrappersImpl, Int64 wrapperId, ObjectHandleOnStack instance, CreateComInterfaceFlags flags, IntPtr& retValue)
            //    at System.Runtime.InteropServices.ComWrappers.TryGetOrCreateComInterfaceForObjectInternal(ComWrappers impl, Object instance, CreateComInterfaceFlags flags, IntPtr& retValue)
            //    at System.Runtime.InteropServices.ComWrappers.GetOrCreateComInterfaceForObject(Object instance, CreateComInterfaceFlags flags)
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForABI(Object obj, Guid iid)
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForMarshaling(Object obj, Guid iid)
            //    at WinRT.MarshalInspectable`1.CreateMarshaler2(T o, Guid iid, Boolean unwrapObject)
            //    at WinRT.MarshalInterface`1.CreateMarshaler2(T value, Guid iid)
            //    at Windows.Devices.Geolocation.Geopath._IGeopathFactoryMethods.Create(IObjectReference _obj, IEnumerable`1 positions)
            //    at Windows.Devices.Geolocation.Geopath..ctor(IEnumerable`1 positions)

            MapStyleSheet.Combine([MapStyleSheet.Aerial()]); // MapStyleSheet is a reference type
            // System.InvalidCastException: Specified cast is not valid.
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForABI(Object obj, Guid iid)
            //    at WinRT.ComWrappersSupport.CreateCCWForObjectForMarshaling(Object obj, Guid iid)
            //    at WinRT.MarshalInspectable`1.CreateMarshaler2(T o, Guid iid, Boolean unwrapObject)
            //    at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)
            //    at WinRT.MarshalInterface`1.CreateMarshaler2(T value, Guid iid)
            //    at ABI.Windows.UI.Xaml.Controls.Maps.IMapStyleSheetStaticsMethods.Combine(IObjectReference _obj, IEnumerable`1 styleSheets)
            //    at Windows.UI.Xaml.Controls.Maps.MapStyleSheet.Combine(IEnumerable`1 styleSheets)

            MapStyleSheet.Combine(new MapStyleSheet[] { MapStyleSheet.Aerial() }); 
            // works when AllowUnsafeBlocks=true, InvalidCastException otherwise

Expected behavior

No exceptions

Version Info

net9.0 rc2, Windows SDK 26100

Additional context

Creating a Geopath in WinUI3 works as expected. (MapStyleSheet is not available in WinUI3)

[dongle-the-gadget]

CsWinRT does not yet support collection expressions in AOT mode. As for the reference type array, it works with unsafe code because CsWinRT needs that to generate AOT shims.

The value-type-array error does look to be an oversight though. cc Manodasan Wignarajah (@manodasanW)

[manodasanW]

We didn't initially support boxing arrays using IReferenceArray due to we couldn't make it work with non-blittable scenarios on AOT. But I am working on a change to enable it for blittable scenarios such as this one.

In the meantime, you should be able to use a list rather than an array or collection expression and it should work.

[devsko]

I tried new Geopath(new List<BasicGeoposition>() { new(0, 0, 0) }); which gives the exact same exception as the one with collection expression.
On WinUI3 all of them work perfectly.

[manodasanW]

Can you confirm the version of the .NET 9 SDK you are using? And to confirm, do you have AllowUnsafeBlocks enabled?

[devsko]

It is 9.0.100-rc.2.24474.11
I uploaded the repro https://github.com/devsko/App10

[Gaoyifei1011]

#1846

Are the internal anomalous causes of the two issues consistent?

-------------------------------------

这俩个问题的内部异常原因是一致的吗？

[Sergio0694]

This was resolved by #1878, closing this.

[devsko]

Sergio Pedri (@Sergio0694) This still doesn't work in CsWinRT 2.2.0 (Windows SDK 10.0.26100.57)

[dongle-the-gadget]

The fix is in 2.3 (although it's not technically a fix but a workaround that it warns on existing incompatible code instead of letting it fail during runtime)

[Sergio0694]

It also collects vtables for supported collection expressions (eg. when targeting concrete types or mutable interfaces).

[devsko]

Is there an ETA for version 2.3?

[devsko]

This is still not working with the 2.3 preview version (Windows SDK 10.0.26100.73-preview)

new Geopath((BasicGeoposition[])[new(0, 0, 0)]); // System.NotSupportedException: Cannot provide IReferenceArray`1 support for element type 'Windows.Devices.Geolocation.BasicGeoposition'.
new Geopath(new BasicGeoposition[] { new(0, 0, 0) }); // System.NotSupportedException: Cannot provide IReferenceArray`1 support for element type 'Windows.Devices.Geolocation.BasicGeoposition'.
new Geopath(new List<BasicGeoposition>() { new(0, 0, 0) }); // System.InvalidCastException: 'Failed to create a CCW for object of type 'System.Collections.Generic.List`1[Windows.Devices.Geolocation.BasicGeoposition]' for interface with IID '922399A8-0093-5009-A8D2-F87B0EAE75F5': the specified cast is not valid.'

The only way i could find to work around is to create a IEnumerable<BasicGeoposition> implementing wrapper class (in version 2.3 i also have to ignore the new warning).

[dongle-the-gadget]

Does adding GeneratedWinRTExposedTypeAttribute on the List help?