[ComInterfaceGenerator] Support PreserveSig on methods

[AaronRobinsonMSFT]

Consider the following API:

[GeneratedComInterface, Guid("B4BE3BD0-3766-4626-B46D-9551B6795CEC")]
public partial interface IEnum
{
    [PreserveSig]
    int Next(uint celt, out uint pceltFetched);
}

The generator attempts to marshal the final out, pceltFetched, instead of returning the HRESULT. It also adds an extra argument? I assume there is some confusion about signature generation when PreserveSig is mentioned.

[System.Runtime.InteropServices.DynamicInterfaceCastableImplementationAttribute]
file unsafe partial interface InterfaceImplementation : global::LibraryImportGeneratorSample.IEnum
{
    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Interop.ComInterfaceGenerator", "42.42.42.42")]
    [System.Runtime.CompilerServices.SkipLocalsInitAttribute]
    int global::LibraryImportGeneratorSample.ICorPublishAppDomainEnum.Next(uint celt, out uint pceltFetched)
    {
        var(__this, __vtable_native) = ((System.Runtime.InteropServices.Marshalling.IUnmanagedVirtualMethodTableProvider)this).GetVirtualMethodTableInfoForKey(typeof(global::LibraryImportGeneratorSample.IEnum));
        System.Runtime.CompilerServices.Unsafe.SkipInit(out pceltFetched);
        int __retVal;
        int __invokeRetVal;
        // Pin - Pin data in preparation for calling the P/Invoke.
        fixed (uint* __pceltFetched_native = &pceltFetched)
        {
            __invokeRetVal = ((delegate* unmanaged<void*, uint, uint*, int*, int> )__vtable_native[4])(__this, celt, __pceltFetched_native, &__retVal);
        }

        System.GC.KeepAlive(this);
        // Unmarshal - Convert native data to managed data.
        System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
        return __retVal;
    }
}

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Issue Details

---

Consider the following API:

[GeneratedComInterface, Guid("B4BE3BD0-3766-4626-B46D-9551B6795CEC")]
public partial interface IEnum
{
    [PreserveSig]
    int Next(uint celt, out uint pceltFetched);
}

The generator attempts to marshal the final out, pceltFetched, instead of returning the HRESULT. It also adds an extra argument? I assume there is some confusion about signature generation when PreserveSig is mentioned.

[System.Runtime.InteropServices.DynamicInterfaceCastableImplementationAttribute]
file unsafe partial interface InterfaceImplementation : global::LibraryImportGeneratorSample.IEnum
{
    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Interop.ComInterfaceGenerator", "42.42.42.42")]
    [System.Runtime.CompilerServices.SkipLocalsInitAttribute]
    int global::LibraryImportGeneratorSample.ICorPublishAppDomainEnum.Next(uint celt, out uint pceltFetched)
    {
        var(__this, __vtable_native) = ((System.Runtime.InteropServices.Marshalling.IUnmanagedVirtualMethodTableProvider)this).GetVirtualMethodTableInfoForKey(typeof(global::LibraryImportGeneratorSample.IEnum));
        System.Runtime.CompilerServices.Unsafe.SkipInit(out pceltFetched);
        int __retVal;
        int __invokeRetVal;
        // Pin - Pin data in preparation for calling the P/Invoke.
        fixed (uint* __pceltFetched_native = &pceltFetched)
        {
            __invokeRetVal = ((delegate* unmanaged<void*, uint, uint*, int*, int> )__vtable_native[4])(__this, celt, __pceltFetched_native, &__retVal);
        }

        System.GC.KeepAlive(this);
        // Unmarshal - Convert native data to managed data.
        System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
        return __retVal;
    }
}

Author:	AaronRobinsonMSFT
Assignees:	-
Labels:	area-System.Runtime.InteropServices, source-generator
Milestone:	8.0.0