Implement unmanaged-to-managed direction for vtable stub generator

[jkoritzinsky]

Implement the unmanaged-to-managed direction for stubs generated with the VTableIndexStubGenerator.

This PR also includes a design doc for how to handle exception handling at the unmanaged-to-managed boundary, which this PR implements.

Generated Code (NativeToManagedStubs.g.cs)

// <auto-generated/>
namespace ComInterfaceGenerator.Tests
{
    internal unsafe partial class NativeExportsNE
    {
        internal unsafe partial class ImplicitThis
        {
            internal unsafe partial interface INativeObject
            {
                internal unsafe partial interface Native
                {
                    [System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute]
                    internal static int ABI_GetData(void* __this_native)
                    {
                        global::ComInterfaceGenerator.Tests.NativeExportsNE.ImplicitThis.INativeObject @this;
                        int __retVal = default;
                        // Unmarshal - Convert native data to managed data.
                        @this = System.Runtime.InteropServices.IUnmanagedVirtualMethodTableProvider<byte>.GetObjectForUnmanagedWrapper<global::ComInterfaceGenerator.Tests.NativeExportsNE.ImplicitThis.INativeObject>(__this_native);
                        __retVal = @this.GetData();
                        return __retVal;
                    }
                }
            }
        }
    }
}
namespace ComInterfaceGenerator.Tests
{
    internal unsafe partial class NativeExportsNE
    {
        internal unsafe partial class ImplicitThis
        {
            internal unsafe partial interface INativeObject
            {
                internal unsafe partial interface Native
                {
                    [System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute]
                    internal static void ABI_SetData(void* __this_native, int x)
                    {
                        global::ComInterfaceGenerator.Tests.NativeExportsNE.ImplicitThis.INativeObject @this;
                        // Unmarshal - Convert native data to managed data.
                        @this = System.Runtime.InteropServices.IUnmanagedVirtualMethodTableProvider<byte>.GetObjectForUnmanagedWrapper<global::ComInterfaceGenerator.Tests.NativeExportsNE.ImplicitThis.INativeObject>(__this_native);
                        @this.SetData(x);
                    }
                }
            }
        }
    }
}

Generated code (PopulateVTable.g.cs)

// <auto-generated/>
namespace ComInterfaceGenerator.Tests
{
    internal unsafe partial class NativeExportsNE
    {
        internal unsafe partial class ImplicitThis
        {
            internal unsafe partial interface INativeObject
            {
                internal unsafe partial interface Native
                {
                    internal static void PopulateUnmanagedVirtualMethodTable(System.Span<nint> vtable)
                    {
                        vtable[0] = (nint)(delegate* unmanaged<void*, int> )&ABI_GetData;
                        vtable[1] = (nint)(delegate* unmanaged<void*, int, void> )&ABI_SetData;
                    }
                }
            }
        }
    }
}

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Issue Details

---

Implement the unmanaged-to-managed direction for stubs generated with the VTableIndexStubGenerator.

This PR also includes a design doc for how to handle exception handling at the unmanaged-to-managed boundary, which this PR will also implement.

TODO:

• Update custom marshalling model to work in the reverse direction.
• Update any other hard-coded marshallers that need to support the reverse direction.
• Implement the EH interop spec as specified in this PR.

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

[AaronRobinsonMSFT]

Can you share an example of what the generated source looks like?

[jkoritzinsky]

Once I've done more work and gotten this PR to at least some semblance of green, I'll add some example generated code to the top of this PR.

[jkoritzinsky]

I've pushed all of the changes to this PR, but I'm going to spin off some of these commits into separate PRs to make them more reviewable. I'll mark this as ready for review once those PRs are merged.

[AaronRobinsonMSFT]

Please give @elinor-fung a chance to review this, but I am good.

[jkoritzinsky]

All test failures are unrelated. @elinor-fung any more feedback before I merge this?

[elinor-fung]

I think it would still be helpful to put examples of the generated source in the PR description. Beyond the PR itself, I have found it helpful when looking through previous changes when reworking (or breaking) things when we were working on LibraryImport.

I think we also need tests that would have caught the exception marshalling wiring (fine with that in a separate change) .

[jkoritzinsky]

I'll add the runtime tests for ExceptionMarshalling in a separate change.

[elinor-fung]

Thanks for adding those generated code examples!

[jkoritzinsky]

Failure is unrelated.