IAudioSessionManager2::GetSessionEnumerator missing parameter

[Sean Yu]

IAudioSessionManager2::GetSessionEnumerator should have a parameter in document. But in generated code:
winmdroot.Media.Audio.IAudioSessionEnumerator GetSessionEnumerator();
And I check the SDK win32metadata, GetSessionEnumerator have a [out] [retval] parameter.
So the parameter is missing.

NativeMethods.txt content:

IAudioSessionControl
IAudioSessionControl2
IAudioSessionEnumerator
IAudioSessionEvents
IAudioSessionManager
IAudioSessionManager2
IAudioSessionNotification
IAudioVolumeLevel
IAudioVolumeDuckNotification

NativeMethods.json content:

{
  "$schema": "https://aka.ms/CsWin32.schema.json",
  "public": true
}

• CsWin32 version: 0.3.49-beta
• Win32Metadata version: 58.0.18-preview
• Target Framework: .NET 7
• LangVersion: 12

[Andrew Arnott]

This is by design. The method is declared like this in the metadata:

unsafe HRESULT GetSessionEnumerator([Out][RetVal] IAudioSessionEnumerator* SessionEnum);

Note the [retval] attribute on the out parameter. That's an indicator that a projection may choose to move the out parameter to the return value position. In .NET, this is the default behavior for COM interfaces, and CsWin32 follows the same pattern.

[Rafael Rivera]

It's not missing an argument. CsWin32 is performing return value transformation here--note how the generated method is returning IAudioSessionEnumerator.

You can preserve the original signature by modifying NativeMethods.json (or creating one if it doesn't exist):

{
    "$schema": "https://aka.ms/CsWin32.schema.json",
    "comInterop": {
        "preserveSigMethods": [
            "IAudioSessionEnumerator.GetSessionEnumerator"
        ]
    }
}

[Rafael Rivera]

Drat, @AArnott beat me to it!

[Andrew Arnott]

@riverar: I'll slow down. I love it when you respond to these issues. :)