Marshal.GetObjectForNativeVariant with IRecordInfo doesn't match netfx behaviour

[hughbe]

From dotnet/corefx#31461

[Fact]
[PlatformSpecific(TestPlatforms.Windows)]
[ActiveIssue()]
public void GetObjectForNativeVariant_Record_ReturnsExpected()
{
    int record = 10;
    var recordInfo = new RecordInfo { Guid = typeof(int).GUID };
    IntPtr pRecord = Marshal.AllocHGlobal(Marshal.SizeOf<int>());
    IntPtr pRecordInfo = Marshal.GetComInterfaceForObject<RecordInfo, IRecordInfo>(recordInfo);
    try
    {
        Marshal.StructureToPtr(record, pRecord, fDeleteOld: false);

        Variant variant = CreateVariant(VT_RECORD, new UnionTypes
        {
            _record = new Record
            {
                _record = pRecord,
                _recordInfo = pRecordInfo
            }
        });
        Assert.Equal(10, GetObjectForNativeVariant(variant));
        GetObjectForNativeVariant_NestedVariant_ReturnsExpected(variant, record);

        variant.m_Variant.vt |= VT_BYREF;
        Assert.Equal(10, GetObjectForNativeVariant(variant));
    }
    finally
    {
        Marshal.DestroyStructure<int>(pRecord);
        Marshal.FreeHGlobal(pRecord);
        Marshal.Release(pRecordInfo);
    }
}

This passes with netfx

On netcoreapp:

Discovering: System.Runtime.InteropServices.Tests
  Discovered:  System.Runtime.InteropServices.Tests
  Starting:    System.Runtime.InteropServices.Tests
     System.Runtime.InteropServices.Tests.GetObjectForNativeVariantTests.GetObjectForNativeVariant_Record_ReturnsExpect
  ed [FAIL]
        System.ArgumentException : The specified record cannot be mapped to a managed value class.
        Stack Trace:
              at System.Runtime.InteropServices.Marshal.GetObjectForNativeVariant(IntPtr pSrcNativeVariant)
           C:\Users\hughb\Documents\GitHub\corefx\src\System.Runtime.InteropServices\tests\System\Runtime\InteropServic
  es\Marshal\GetObjectForNativeVariantTests.cs(1027,0): at System.Runtime.InteropServices.Tests.GetObjectForNativeVaria
  ntTests.GetObjectForNativeVariant(Variant variant)
           C:\Users\hughb\Documents\GitHub\corefx\src\System.Runtime.InteropServices\tests\System\Runtime\InteropServic
  es\Marshal\GetObjectForNativeVariantTests.cs(700,0): at System.Runtime.InteropServices.Tests.GetObjectForNativeVarian
  tTests.GetObjectForNativeVariant_Record_ReturnsExpected()
  Finished:    System.Runtime.InteropServices.Tests

[jeffschwMSFT]

@AaronRobinsonMSFT

[AaronRobinsonMSFT]

This is an annoying issue and what to do isn't entirely obvious. What should probably happen is support querying the registry for the type, but in this case that entire code path has been removed. In .NET Framework this path was relying on TLB generation to get the COM layout based on the managed metadata. Since that entire code path has been removed it seems like the correct solution here is by-design.

I am torn because we could make this work for blittable types like the test is using. I am going to close this for now and wait for additional feedback from users before doing the work to actually support aspects of this.

[jkotas]

We should delete ActiveIssue link from the test to this issue before closing this. We do not want to have ActiveIssue links to closed bugs.

[hughbe]

So was looking at things in dotnet/winforms#3197

I sort of think we should really be throwing PlatformNotSupportedException if we encounter VT_RECORD in variants.

Currently the handling is completely broken and doesn't work.

/cc @weltkante

[AaronRobinsonMSFT]

@hughbe I would file a new bug with the desired behavior. Feel free to reference this issue.