🍒[5.7] Remove the need for convenience keyword for delegating actor initializers
#59741
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convenience keyword for delegating actor initializersconvenience keyword for delegating actor initializers
DougGregor
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This is possible because actors do not support inheritance. There is one specific exception to that rule, which is that an actor can inherit from `NSObject` just to support ObjC interop. This means an actor is effectively a final class. resolves rdar://87568153
When synthesizing the default initializer for an actor, we'd sometimes hit a cycle when that initializer needs to chain to NSObject.init. The cycle only happens because we ask if the initializer we're trying to synthesize is a convenience init in a scenario which only applies to non-final classes. Since all actors are effectively "final" classes, it's valid to workaround the cycle by only asking that initializer question for non-final classes, thus breaking the cycle.
it should not matter whether an initializer is delegating or not when importing a library. this test helps make sure that stays true.
A public designated initializer of a class would have its allocating entry-point serialized in the module, meaning with `-O` that entry-point can get inlined into programs linking against that module. Once that entry-point is inlined, the program will _require_ that it remain non-delegating, because it will depend on the 2nd entry-point (for actual initializing) to be in the library. As a result of this change, public initializers of an actor should be resilient in a library, whether their underlying implementation is delegating or not.
When I began removing `convenience` from actor inits, I thought it would be ok for an actor's extensions to be non-delegating. But that's wrong, because the actor could be in a resilient module and still have its properties change between stored and computed, meaning that there isn't a practical way to allow this, unless if the extension and the actor are in the same file. For now, just re-ban this behavior before anybody notices :)
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Cherry-pick of #41083 and #59828
This is part of SE-327 and includes new warnings for the
conveniencekeyword appearing and has a fix-it to delete it. Those warnings turn into an error in Swift 6.Description: As part of SE-327, the
conveniencekeyword is no longer required for delegating actor initializers (the presence of it becomes an error in Swift 6). This means the initializers work similarly to structs, e.g., a non-delegating init can now appear in the extension of an actor.Risk: Medium. This PR introduces an ABI break for any libraries that had a public
actorinit. Specifically, if the library was compiled with Swift 5.6 or 5.5, any program compiled with optimizations enabled and linked against that library will be dependent on the initializer's delegating status remaining fixed. For example, if the library authors change the implementation to no-longer delegate, the Swift <5.7 program will need to be recompiled, or else there will be a missing symbol error. For Swift 5.7+ we now specifically guarantee that changing the implementation of the init to delegate or not won't break existing programs.Importance: High. The longer we wait to make this ABI break, the worse it will become.
Review by: Doug Gregor
Testing: PR testing
Original PR: #41083 #59828
Radar: rdar://87567878