COM interface return type incorrect

[lilhoser]

When NativeMethods.txt: IAttachmentExecute, the generated COM interface has functions with incorrect return types (void instead of HRESULT):

An example:

/// <summary>Provides a Boolean test that can be used to make decisions based on the attachment's execution policy.</summary>
/// <returns>
/// <para>Type: <b>HRESULT</b> Returns one of the following values.</para>
/// <para></para>
/// <para>This doc was truncated.</para>
/// </returns>
/// <remarks>
/// <para><b>IAttachmentExecute::CheckPolicy</b> examines a set of properties known collectively as <i>evidence</i>. Anything used to determine trust level is considered evidence. These properties are set using the following methods.</para>
/// <para></para>
/// <para>This doc was truncated.</para>
/// <para><see href="https://learn.microsoft.com/windows/win32/api/shobjidl_core/nf-shobjidl_core-iattachmentexecute-checkpolicy#">Read more on docs.microsoft.com</see>.</para>
/// </remarks>
void CheckPolicy();

When I set "allowMarshaling": false it generates correct prototypes:

			[UnmanagedCallersOnly(CallConvs = new []{
typeof(CallConvStdcall)}
)]
			private static winmdroot.Foundation.HRESULT CheckPolicy(IAttachmentExecute* pThis)
			{
				try
				{
					winmdroot.Foundation.HRESULT __hr = ComHelpers.UnwrapCCW(pThis, out Interface __object);
					if (__hr.Failed)
					{
						return __hr;
					}
					return __object.CheckPolicy();
				}
				catch (Exception ex)
				{
					return (winmdroot.Foundation.HRESULT)ex.HResult;
				}
			}

[AArnott]

The signatures are not incorrect. They are simply declared in the default .NET interop mode where the HRESULT is hidden, and error codes are thrown in a COMException.

If you want to see the HRESULT return codes, you can opt into preservesig mode with a NativeMethods.json file like this:

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