Handle PreserveSig=false

[elinor-fung]

• Add marshaller for checking HR and throwing on errror
• Handle transforming return value to last out param

cc @AaronRobinsonMSFT @jkoritzinsky

No return value

public static partial void NoReturnValue(int i)
{
    unsafe
    {
        int __invokeRetVal = default;
        //
        // Invoke
        //
        __invokeRetVal = NoReturnValue__PInvoke__(i);
        //
        // Unmarshal
        //
        System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
    }
}

[System.Runtime.InteropServices.DllImportAttribute("NativeExportsNE", EntryPoint = "hresult_return")]
extern private static unsafe int NoReturnValue__PInvoke__(int i);

int as return

public static partial int Int_AsReturn(int i)
{
    unsafe
    {
        int __retVal = default;
        int __invokeRetVal = default;
        //
        // Invoke
        //
        __invokeRetVal = Int_AsReturn__PInvoke__(i, &__retVal);
        //
        // Unmarshal
        //
        System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("NativeExportsNE", EntryPoint = "hresult_out_int")]
extern private static unsafe int Int_AsReturn__PInvoke__(int i, int *__retVal);

UTF-16 string as return

public static partial string String_AsReturn(int i)
{
    unsafe
    {
        string __retVal = default;
        ushort *__retVal_gen_native = default;
        int __invokeRetVal = default;
        try
        {
            //
            // Invoke
            //
            __invokeRetVal = String_AsReturn__PInvoke__(i, &__retVal_gen_native);
            //
            // Unmarshal
            //
            System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
            __retVal = __retVal_gen_native == null ? null : new string ((char *)__retVal_gen_native);
        }
        finally
        {
            //
            // Cleanup
            //
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__retVal_gen_native);
        }

        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("NativeExportsNE", EntryPoint = "hresult_out_ushort_string")]
extern private static unsafe int String_AsReturn__PInvoke__(int i, ushort **__retVal);

int array as return

public static partial int[] IntArray_AsReturn(int i)
{
    unsafe
    {
        int[] __retVal = default;
        int *__retVal_gen_native = default;
        int __invokeRetVal = default;
        try
        {
            //
            // Invoke
            //
            __invokeRetVal = IntArray_AsReturn__PInvoke__(i, &__retVal_gen_native);
            //
            // Unmarshal
            //
            System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
            if (__retVal_gen_native != null)
            {
                __retVal = new int[4];
                new System.Span<int>(__retVal_gen_native, __retVal.Length).CopyTo(__retVal);
            }
            else
                __retVal = null;
        }
        finally
        {
            //
            // Cleanup
            //
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__retVal_gen_native);
        }

        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("NativeExportsNE", EntryPoint = "hresult_out_int_array")]
extern private static unsafe int IntArray_AsReturn__PInvoke__(int i, int **__retVal);

SafeHandle as return

public static partial global::DllImportGenerator.IntegrationTests.NativeExportsNE.PreserveSig.DummySafeHandle SafeHandle_AsReturn(int hr)
{
    unsafe
    {
        global::DllImportGenerator.IntegrationTests.NativeExportsNE.PreserveSig.DummySafeHandle __retVal = default;
        global::System.IntPtr __retVal_gen_native = default;
        int __invokeRetVal = default;
        //
        // Setup
        //
        __retVal = System.Runtime.InteropServices.MarshalEx.CreateSafeHandle<global::DllImportGenerator.IntegrationTests.NativeExportsNE.PreserveSig.DummySafeHandle>();
        try
        {
            //
            // Invoke
            //
            __invokeRetVal = SafeHandle_AsReturn__PInvoke__(hr, &__retVal_gen_native);
            //
            // Unmarshal
            //
            System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);
        }
        finally
        {
            //
            // GuaranteedUnmarshal
            //
            System.Runtime.InteropServices.MarshalEx.SetHandle(__retVal, __retVal_gen_native);
        }

        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("NativeExportsNE", EntryPoint = "hresult_out_handle")]
extern private static unsafe int SafeHandle_AsReturn__PInvoke__(int hr, global::System.IntPtr*__retVal);

[jkoritzinsky]

Now that we're adding tests that throw exceptions, we should make sure that we don't forget to add the cleanup exception handling to the stubs.