The proposal does call out the possibility of a breakage if you're relying on the previous behaviour, but you're right, it doesn't explicitly talk about exclusivity violation, my apologies! I will amend the proposal to mention it.
It seems to me that didSet(oldValue) should trigger an access conflict too, at least based on this post:
but I am not qualified enough to provide an accurate answer on this topic. cc @Andrew_Trick
I assume Swift 5.2 would have crashed on this without
didSetat all (though I don't have it accessible at the moment to test)
Yes, it will trigger an access conflict, if there isn’t a didSet.