[6.1]Revert [ConformanceLookup] Don't allow skipping inherited unavailable conformances in favor of explicit available ones. #79596
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@swift-ci please test source compatibility |
bnbarham
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Feb 25, 2025
hborla
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@swift-ci please test macOS |
hborla
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Explanation: [ConformanceLookup] Don't allow skipping inherited unavailable conformances in favor of explicit available ones. #75135 exposed a few incorrect
Sendableannotations in libraries. Most notably,FormatterinFoundationhas an unavailable conformance toSendable, while subclasses includingDateFormatterhave an available conformance toSendable. This is not supported; types can only have one conformance to a protocol. If a superclass wants to allow subclasses to have differing availability on a particular protocol conformance, the subclass should have no conformance to that protocol at all. The fix is to remove the unavailableSendableconformance onFormatterin Foundation. This revert is a workaround until libraries have time to update their conformances.This impact is programmers will miss out on redundant
Sendableconformance warnings, and observe unexpected behavior for code that declares both an unavailable conformance and an available conformance toSendable(which is already the case in Swift 6.0).Note that I did not revert [Concurrency] Don't warn about re-stating inherited unavailable conformances to
Sendable. #75359. It should not have any impact. The Swift 6.0 compiler has the exact same set of reverts.Scope: Only impacts redundant conformances to
Sendablewhere at least one of the conformances is unavailable.Issues: Swift 6.1 regression in Sendable checking #78635
Original PRs: There is no
mainPR for this revert. This revert is forrelease/6.1only. The compiler change is correct, but there are a handful of incorrectSendableannotations in libraries that should be fixed before this change lands to avoid source compatibility issues in client projects.Risk: Low; this change restores the behavior before [ConformanceLookup] Don't allow skipping inherited unavailable conformances in favor of explicit available ones. #75135 and [Conformance] Always downgrade redundant conformances to marker protocols to a warning. #75425. These changes were reverted from
release/6.0for a different reasonTesting: N/A
Reviewers: @bnbarham @DougGregor