[.NET 6] Linker may not preserve exported methods with overrides

[sbomer]

This check for overrides happens before MarkStep, when the linker has not built type hierarchy info. Even when this changes to run during MarkStep with #11374, there is no guarantee that the override info will be complete, so it will likely neglect to preserve some exported methods that have overrides which aren't discovered yet.

https://github.com/xamarin/xamarin-macios/blob/50b68d4aab0a1099113a68c04aad5a77592b6e52/tools/linker/MarkNSObjects.cs#L84-L91

It seems like this could be changed to walk up the type hierarchy instead (though this would require looking at base methods for many unannotated methods), or it could be cached as part of some custom type map logic that pre-loads assemblies as mentioned in #11447. (I am filing this as a separate issue because it seems like a correctness concern, not just a perf optimization).

[spouliot]

iirc that has been fixed a while ago, at least since 045ccaf
@sbomer what there anything missing ?

[sbomer]

Yup, this was fixed in that change. CoreTypeMapStep now builds the type hierarchy info before this override check.