[ComInterfaceGenerator] PreserveSig with collection return type will not properly marshal back to caller

[jtschuster]

This is probably not a realistic situation, but we may want to fix it or warn when the [PreserveSig] return value unmarshaller doesn't take an int as the unmanaged type.

This method definition

        [PreserveSig]
        [return: MarshalUsing(CountElementName = nameof(size))]
        StatelessCollection<StatelessType> ReturnPreserveSig(int size);

will generate this unmanaged to managed method

    internal static global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> ABI_ReturnPreserveSig(System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch* __this_native, int size)
    {
        global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement @this = default;
        global::SharedTypes.ComInterfaces.StatelessCollection<global::SharedTypes.ComInterfaces.StatelessType> __retVal = default;
        global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> __retVal_native = default;
        // Setup - Perform required setup.
        int __retVal_native__numElements;
        System.Runtime.CompilerServices.Unsafe.SkipInit(out __retVal_native__numElements);
        try
        {
            // Unmarshal - Convert native data to managed data.
            @this = System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch.GetInstance<global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement>(__this_native);
            __retVal = @this.ReturnPreserveSig(size);
            // Marshal - Convert managed data to native data.
            __retVal_native = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.AllocateContainerForUnmanagedElements(__retVal, out __retVal_native__numElements);
            {
                System.ReadOnlySpan<global::SharedTypes.ComInterfaces.StatelessType> __retVal_native__managedSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetManagedValuesSource(__retVal);
                System.Span<nint> __retVal_native__nativeSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetUnmanagedValuesDestination(__retVal_native, __retVal_native__numElements);
                __retVal_native__nativeSpan.Clear();
                ; // Should be a for loop here that marshals elements
            }
        }
        catch (System.Exception __exception)
        {
            __retVal_native = System.Runtime.InteropServices.Marshalling.ExceptionAsDefaultMarshaller<global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType>>.ConvertToUnmanaged(__exception);
        }

        return __retVal_native;
    }

For comparison, a regular managed return value

        [return: MarshalUsing(CountElementName = nameof(size))]
        StatelessCollection<StatelessType> Return(int size);

Generates this unmanaged to managed stub

    internal static int ABI_Return(System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch* __this_native, int size, global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType>* __invokeRetValUnmanaged__param)
    {
        global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement @this = default;
        ref global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetValUnmanaged = ref *__invokeRetValUnmanaged__param;
        global::SharedTypes.ComInterfaces.StatelessCollection<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetVal = default;
        int __retVal = default;
        // Setup - Perform required setup.
        int __invokeRetValUnmanaged__numElements;
        System.Runtime.CompilerServices.Unsafe.SkipInit(out __invokeRetValUnmanaged__numElements);
        try
        {
            // Unmarshal - Convert native data to managed data.
            __retVal = 0; // S_OK
            @this = System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch.GetInstance<global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement>(__this_native);
            __invokeRetVal = @this.Return(size);
            // Marshal - Convert managed data to native data.
            __invokeRetValUnmanaged = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.AllocateContainerForUnmanagedElements(__invokeRetVal, out __invokeRetValUnmanaged__numElements);
            {
                System.ReadOnlySpan<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetValUnmanaged__managedSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetManagedValuesSource(__invokeRetVal);
                System.Span<nint> __invokeRetValUnmanaged__nativeSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetUnmanagedValuesDestination(__invokeRetValUnmanaged, __invokeRetValUnmanaged__numElements);
                __invokeRetValUnmanaged__nativeSpan.Clear();
                for (int __i0 = 0; __i0 < __invokeRetValUnmanaged__managedSpan.Length; ++__i0)
                {
                    __invokeRetValUnmanaged__nativeSpan[__i0] = global::SharedTypes.ComInterfaces.StatelessTypeMarshaller.ManagedToUnmanaged.ConvertToUnmanaged(__invokeRetValUnmanaged__managedSpan[__i0]);
                }
            }
        }
        catch (System.Exception __exception)
        {
            __retVal = System.Runtime.InteropServices.Marshalling.ExceptionAsHResultMarshaller<int>.ConvertToUnmanaged(__exception);
        }

        return __retVal;
    }

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Issue Details

---

This is probably not a realistic situation, but we may want to fix it or warn when the [PreserveSig] return value unmarshaller doesn't take an int as the unmanaged type.

This method definition

        [PreserveSig]
        [return: MarshalUsing(CountElementName = nameof(size))]
        StatelessCollection<StatelessType> ReturnPreserveSig(int size);

will generate this unmanaged to managed method

    internal static global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> ABI_ReturnPreserveSig(System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch* __this_native, int size)
    {
        global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement @this = default;
        global::SharedTypes.ComInterfaces.StatelessCollection<global::SharedTypes.ComInterfaces.StatelessType> __retVal = default;
        global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> __retVal_native = default;
        // Setup - Perform required setup.
        int __retVal_native__numElements;
        System.Runtime.CompilerServices.Unsafe.SkipInit(out __retVal_native__numElements);
        try
        {
            // Unmarshal - Convert native data to managed data.
            @this = System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch.GetInstance<global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement>(__this_native);
            __retVal = @this.ReturnPreserveSig(size);
            // Marshal - Convert managed data to native data.
            __retVal_native = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.AllocateContainerForUnmanagedElements(__retVal, out __retVal_native__numElements);
            {
                System.ReadOnlySpan<global::SharedTypes.ComInterfaces.StatelessType> __retVal_native__managedSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetManagedValuesSource(__retVal);
                System.Span<nint> __retVal_native__nativeSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetUnmanagedValuesDestination(__retVal_native, __retVal_native__numElements);
                __retVal_native__nativeSpan.Clear();
                ; // Should be a for loop here that marshals elements
            }
        }
        catch (System.Exception __exception)
        {
            __retVal_native = System.Runtime.InteropServices.Marshalling.ExceptionAsDefaultMarshaller<global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType>>.ConvertToUnmanaged(__exception);
        }

        return __retVal_native;
    }

For comparison, a regular managed return value

        [return: MarshalUsing(CountElementName = nameof(size))]
        StatelessCollection<StatelessType> Return(int size);

Generates this unmanaged to managed stub

    internal static int ABI_Return(System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch* __this_native, int size, global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType>* __invokeRetValUnmanaged__param)
    {
        global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement @this = default;
        ref global::SharedTypes.ComInterfaces.NativeCollection<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetValUnmanaged = ref *__invokeRetValUnmanaged__param;
        global::SharedTypes.ComInterfaces.StatelessCollection<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetVal = default;
        int __retVal = default;
        // Setup - Perform required setup.
        int __invokeRetValUnmanaged__numElements;
        System.Runtime.CompilerServices.Unsafe.SkipInit(out __invokeRetValUnmanaged__numElements);
        try
        {
            // Unmarshal - Convert native data to managed data.
            __retVal = 0; // S_OK
            @this = System.Runtime.InteropServices.ComWrappers.ComInterfaceDispatch.GetInstance<global::SharedTypes.ComInterfaces.IStatelessCollectionStatelessElement>(__this_native);
            __invokeRetVal = @this.Return(size);
            // Marshal - Convert managed data to native data.
            __invokeRetValUnmanaged = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.AllocateContainerForUnmanagedElements(__invokeRetVal, out __invokeRetValUnmanaged__numElements);
            {
                System.ReadOnlySpan<global::SharedTypes.ComInterfaces.StatelessType> __invokeRetValUnmanaged__managedSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetManagedValuesSource(__invokeRetVal);
                System.Span<nint> __invokeRetValUnmanaged__nativeSpan = global::SharedTypes.ComInterfaces.StatelessCollectionMarshaller<global::SharedTypes.ComInterfaces.StatelessType, nint>.ManagedToUnmanaged.GetUnmanagedValuesDestination(__invokeRetValUnmanaged, __invokeRetValUnmanaged__numElements);
                __invokeRetValUnmanaged__nativeSpan.Clear();
                for (int __i0 = 0; __i0 < __invokeRetValUnmanaged__managedSpan.Length; ++__i0)
                {
                    __invokeRetValUnmanaged__nativeSpan[__i0] = global::SharedTypes.ComInterfaces.StatelessTypeMarshaller.ManagedToUnmanaged.ConvertToUnmanaged(__invokeRetValUnmanaged__managedSpan[__i0]);
                }
            }
        }
        catch (System.Exception __exception)
        {
            __retVal = System.Runtime.InteropServices.Marshalling.ExceptionAsHResultMarshaller<int>.ConvertToUnmanaged(__exception);
        }

        return __retVal;
    }

Author:	jtschuster
Assignees:	-
Labels:	area-System.Runtime.InteropServices
Milestone:	-