[Concurrency] Implement a narrow carve out in the isolation override checking for NSObject.init().
#75748
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override checking for `NSObject.init()` Overriding `NSObject.init()` within a `@MainActor`-isolated type is difficult-to-impossible, especially if you need to call an initializer from an intermediate superclass that is also `@MainActor`-isolated. This won't admit a runtime data-race safety hole, because dynamic isolation checks will be inserted in the @objc thunks under `DynamicActorIsolation`, and direct calls will enforce `@MainActor` as usual.
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ktoso
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Aug 7, 2024
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Overriding
NSObject.init()within a@MainActor-isolated type is difficult-to-impossible, especially if you need to call an initializer from an intermediate superclass that is also@MainActor-isolated. Opt-out tools likeMainActor.assumeIsolatedcannot be applied to things like stored property initialization andsuper.init(), making the issue extremely difficult to work around.This carve-out won't admit a runtime data-race safety hole, because dynamic isolation checks will be inserted in the @objc thunks under
DynamicActorIsolation, and direct calls will enforce@MainActoras usual.Resolves: #75732, rdar://133349184