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Dropping the subclassing adapter while a key-value observer is registered on the view discarded KVO's dynamic subclass, so removing the observer later raised NSRangeException. AppKit registers such observers itself on the first responder, which made apps crash when closing a window.
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Closes #823
SubclassingAdapter::dropresets the view's class unconditionally. If a key-value observer was registered on the view after the adapter was created, this discards KVO'sNSKVONotifying_…subclass while the observer is still registered, and the laterremoveObserver:forKeyPath:raisesNSRangeException. AppKit registers such observers itself on the first responder, so apps crash when their window is closed.With this change, the previous class is only restored if ours is still the view's class. Otherwise the view keeps our subclass and its associated object until it is deallocated.
The new test adds an observer, drops the adapter and removes the observer. It has to run on the main thread, so it uses
harness = false; tell me if you'd prefer it done differently.cargo test -p accesskit_macospasses on Rust 1.87 and on stable. I also tested manually with the same change applied to accesskit_macos 0.26.3 on macOS 27.0.1: the crash no longer happens.