[Concurrency] tighten-up rules about isolated generic parameters #68612
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kavon
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ktoso,
hborla,
slavapestov and
xedin
as code owners
We were missing a check for conformance to `Actor` or `DistributedActor` when an isolated parameter's type is a generic parameter. Previously, if you used a generic parameter constrained to just `AnyActor`, you'd crash the compiler in LowerHopToExecutor because it doesn't know how to obtain the executor for such a value. Since `AnyActor` has no `unownedExecutor` requirement, there's no way to get the executor without emitting code to do dynamic casts down to `Actor` or `DistributedActor`. Rather than have the compiler silently emit dynamic casting, I figured it's best to ban it. This forces people to either do the dynamic casts themselves, or use one of the more specific types to constrain their parameter. For other generic parameters, we would silently treat the function as though it is nonisolated (i.e., as if the `isolated` wasn't written on the parameter at all). resolves rdar://109059544
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@swift-ci please test |
ktoso
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Sep 19, 2023
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Oh right, I guess dynamic casts aren't even permitted on an |
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[Concurrency] tighten-up rules about isolated generic parameters
We were missing a check for conformance to
ActororDistributedActorwhen an isolated parameter's type is a generic parameter.
Previously, if you used a generic parameter constrained to just
AnyActor,you'd crash the compiler in LowerHopToExecutor because it doesn't know
how to obtain the executor for such a value. Since
AnyActorhas nounownedExecutorrequirement, there's no way to get the executor withoutemitting code to do dynamic casts down to
ActororDistributedActor.Rather than have the compiler silently emit dynamic casting, I figured
it's best to ban it. This forces people to either do the dynamic casts
themselves, or use one of the more specific types to constrain their
parameter.
For other generic parameters, we would silently treat the function
as though it is nonisolated (i.e., as if the
isolatedwasn't writtenon the parameter at all).
resolves rdar://109059544