Sema: Change behavior of implied 'Sendable' conformance #74908
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slavapestov
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ktoso,
AnthonyLatsis,
hborla and
xedin
as code owners
A conditional conformance to a protocol does not usually imply
a conformance to the protocol's inherited protocols, because
we have no way to guess what the conditional requirements
should be.
A carveout was added for 'Sendable', so that protocols could
inherit from 'Sendable' retroactively. However, the 'Sendable'
conformance would become conditional, which causes us to
reject a _second_ conditional conformance to such a protocol:
struct G<T> {}
protocol P: Sendable {}
protocol Q: Sendable {}
extension G: P where T: P {}
extension G: Q where T: Q {}
To make this work, tweak the code so that an implied conformance
has the same generic signature as the conforming type, that is,
we force it to be unconditional.
Fixes rdar://122754849
Fixes swiftlang#71544
You can't do this anymore:
struct G<T> {}
protocol P: Sendable {}
extension G: P where T: P {}
Fixes rdar://95695543.
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@swift-ci Please test source compatibility |
xedin
approved these changes
Jul 3, 2024
DougGregor
reviewed
Jul 3, 2024
| @@ -2415,8 +2415,16 @@ checkIndividualConformance(NormalProtocolConformance *conformance) { | |||
| ComplainLoc, diag::unchecked_conformance_not_special, ProtoType); | |||
| } | |||
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| bool allowImpliedConditionalConformance = false; | |||
| if (Proto->isSpecificProtocol(KnownProtocolKind::Sendable)) { | |||
| if (Context.LangOpts.StrictConcurrencyLevel != StrictConcurrency::Complete) | |||
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Should this be checking for Swift 6 instead, so we don't change Swift 5 code that enabled strict checking?
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Today, this gives you a conditional conformance to
Sendablein Swift 5 and 6 language mode:Change this so that in Swift 5 mode, the implied conformance is unconditional:
And ban it outright in Swift 6 mode:
Fixes rdar://95695543.
Fixes rdar://122754849.
Fixes #71544.