Bug: InvalidCastException because failed to create a CCW in AOT for IAsyncOperation<>

[zhuxb711]

Description

An WinRT API described below:

public static class MyClass
{
    public static IAsyncOperation<IReadOnlyList<MyData>> TestAsync ()
    {
        return AsyncInfo.Run((CancelToken) => new ReadOnlyCollection<MyData>([new MyData()]));
    }
}

Everything OK if AOT not enabled. However, once AOT enabled. The caller will get an InvalidCastException. Failed to create a CCW for ReadOnlyCollection<MyData>.

After adding the code below, it works again in AOT.

[assembly: GeneratedWinRTExposedExternalType(typeof(ReadOnlyCollection<MyData>))]

I want to know will this exception be fixed in CsWinRT 2.3 and adding GeneratedWinRTExposedExternalType for the generic collection is just a temporary workaround? Or it's not a bug and we should always use GeneratedWinRTExposedExternalType to every generic collection variant to make it works in AOT?

What is the difference for my case after #1877 collection expression implemented in CsWinRT 2.3 ?

public static IAsyncOperation<IReadOnlyList<MyData>> TestAsync ()
{
    // After CsWinRT 2.3, this will also works?
    // Will we still need GeneratedWinRTExposedExternalType(typeof(ReadOnlyCollection<MyData>)) ?
    return AsyncInfo.Run((CancelToken) => [new MyData()]);
    // return AsyncInfo.Run((CancelToken) => new ReadOnlyCollection<MyData>([new MyData()]));
}

Steps To Reproduce

See code above

Expected Behavior

Should generate the CCW automatically for anything like

IAsyncOperation<IReadOnlyList<>>
IAsyncOperation<IList<>>
IAsyncOperation<IEnumerable<>>
IAsyncOperation<ICollection<>>

Version Info

Microsoft.Windows.CsWinRT 2.2.0

Additional Context

No response

[zhuxb711]

This is not working for me and it seems will not generate the CCW for IReadOnlyList<MyData> or IEnumerable<MyData> automatically. We still need to use GeneratedWinRTExposedExternalType explicitly.

<CsWinRTAotOptimizerEnabled>Auto</CsWinRTAotOptimizerEnabled>

[dongle-the-gadget]

Collection expressions in 2.3 will not work without an explicit type, although I think it should improve CCW type detection.

[zhuxb711]

@dongle-the-gadget 2.3 will work in this situation? When will 2.3 release? It should be released in Jan. 2026.

public static IAsyncOperation<IReadOnlyList<MyData>> TestAsync ()
{
    // [new MyData] --> IReadOnlyList<MyData>
    return AsyncInfo.Run<IReadOnlyList<MyData>>((CancelToken) => [new MyData()]);
}

Indeed, CsWinRT should improve the CCW detection for the following type.

IAsyncOperation<IReadOnlyList<>>
IAsyncOperation<IList<>>
IAsyncOperation<IEnumerable<>>
IAsyncOperation<ICollection<>>

[manodasanW]

Can you try 2.3.0-prerelease.251115.2 to see if it resolves your issue. We are looking at investigating and addressing a couple more bugs before making it stable.

[zhuxb711]

@manodasanW

2.3.0-prerelease.251115.2

// [assembly: GeneratedWinRTExposedExternalType(typeof(ReadOnlyCollection<MyData>))]

Still throw the InvalidCastException if not using GeneratedWinRTExposedExternalType(typeof(ReadOnlyCollection<MyData>)

Failed to create a CCW for object of type 'System.Collections.ObjectModel.ReadOnlyCollection`1[MyData]' for interface with IID 'E12C218A-5D64-5E6E-A4B5-164F2E2215BC': the specified cast is not valid.

I think the root cause should be CsWinRT could not create the CCW for IReadOnlyList<> automatically