[Concurrency] Diagnose captures of self in a task created in deinit.
#75224
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…mances in favor of explicit available ones. The type checker does not support the notion of multiple protocol conformances; there can only be one conformance, and if that conformance is unavailable, you cannot specify your own available conformance. This is important for Sendable checking; if a framework specifies that a type is explicitly not Sendable with an unavailable Sendable conformance, clients cannot ignore Sendable violations involving that type. If a superclass wants to allow subclasses to add a Sendable conformance, it should not declare an unavailable Sendable conformance.
…rom the defining module, and diagnose redundant Sendable conformances. We still allow re-stating inherited unchecked Sendable conformances in subclasses because inherited Sendable conformances are surprising when they opt out of static checking. Otherwise, warning on redundant Sendable conformances nudges programmers toward cleaning up unnecessary retroactive Sendable conformances over time as libraries incrementally add the conformances directly.
Sendable conformances for source compatibility. If conformance lookup always prefers the conformance from the defining module, libraries introducing unavailable Sendable conformances can break source in clients that declare retroactive Sendable conformances. Instead, still prefer the available conformance, and always diagnose the client conformance as redundant (as a warning). Then, when the retroactive conformance is removed, the errors will surface, so the programmer has to take explicit action to experience the source break.
This is done by diagnosing captures of `self` in escaping `sending` or `@Sendable` closures inside a deinit, which almost certainly means `self` will outlive deinit at runtime, which is a fatal error. This is a common mistake to make when creating isolated tasks inside nonisolated deinits to workaround the lack of synchrnous isolated deinits in Swift 6.
hborla
requested review from
ktoso,
AnthonyLatsis,
slavapestov and
xedin
as code owners
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@swift-ci please smoke test |
ktoso
approved these changes
Jul 13, 2024
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@swift-ci please smoke test macOS |
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This is done by diagnosing captures of
selfin escapingsendingor@Sendableclosures inside a deinit, which almost certainly meansselfwill outlive deinit at runtime, which is a fatal error. This is a common mistake to make when creating isolated tasks inside nonisolated deinits to workaround the lack of synchronous isolated deinits in Swift 6.Resolves: #72893
Note that this PR contains the commits from #75135. Only the last commit of this PR is relevant.