Remove CoClass usages from System.Windows.Forms

[kant2002]

This helps make WinForms application more ILLink/NativeAOT-friendly

Fixes #4940

Microsoft Reviewers: Open in CodeFlow

[RussKie]

@JeremyKuhne @AaronRobinsonMSFT may I get you to review this one?

[weltkante]

I've added a few comments with suggestions, note that these apply to all three locations but I only annotated the first occurence since the others are identical.

[AaronRobinsonMSFT]

Overall, I've no real issues with this change as it just makes the veneer over COM class activation explicit. I don't fully get why this needed. However, I'm not plugged into all the NativeAOT work so I could see a case for this change being cheaper than supporting how .NET has traditionally activated a COM class.

[kant2002]

@AaronRobinsonMSFT I suspect that new RCW should be treated in different way by compiler and only for Windows, which is additional complexity. Second option is that RhNewObject would be aware about CoClass, so penalty for new objects would be applied across all object creation. Again, this is what I see from where I'm sitting. This is about only change which is required for WinForms. There exists CoClass in the Accessibility, but that's about it what is needed for making file dialogs works in NativeAOT.

[weltkante]

Looks good with the open discussion about removing the IIDs and calling CoCreateInstance with IID_IUnknown instead which already has a constant.

Also it may be worth moving the CLSID constants into the interop files, after all these are constants from the win32 API. Not sure where they would go though @RussKie

[JeremyKuhne]

Also it may be worth moving the CLSID constants into the interop files, after all these are constants from the win32 API. Not sure where they would go though @RussKie

I'd say under the root in Interop. Following the existing pattern of Interop.CLSID.cs with CLSID being a static class with FileSaveDialog, etc. as statics in it.

Note that there is cost to having these take strings (I don't think it gets optimized away). It might be worth changing these to Guid(uint a, ushort b, ushort c, byte d, byte e, byte f, byte g, byte h, byte i, byte j, byte k), at least long term.

[kant2002]

@JeremyKuhne can you take a look?

[RussKie]

@kant2002 Jeremy is currently OOF, will be back next week.

[JeremyKuhne]

Looks good, thanks!

[RussKie]

🚀

[RussKie]

Thank you all.