Make overloads and witnesses permit @Sendable variance + Make @preconcurrency import hide sendable variance #42273
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Specifically, an override can validly have a parameter type that is not `@Sendable` or a function type that is `@Sendable` even if that contradicts the base declaration. That’s becuase it’s always valid to provide a sendable function when one is not actually needed, but not vice versa.
It previously treated parameters and return types as the same, instead of properly handling variance.
If a type is explicitly non-Sendable, we don’t want to recommend softening errors with `@preconcurrency import` (even thought that would still work), because these probably represent *real* errors that you ought to fix. And at the extreme end of this, if a module is built with `-warn-concurrency` or `-swift-version 6`, *all* of its types should be treated as though they have explicit sendability, since we assume the entire module has been audited. (Eventually, we plan to do this at module build time by actually serializing out unavailable conformances rather than by looking at the settings used to build the module, but we aren’t there quite yet.) Implement this and test it by checking that the preconcurrency sendable tests never recommend adding `@preconcurrency` to an import of `StrictModule`, even when we do the same illegal things with it that cause that remark to be printed for `NonStrictModule`.
`diagnoseAsNonSendableBasedOn()` extracts just the “make a diagnostic sensitive to @preconcurrency import of this type” logic from `diagnoseNonSendableTypes()`. We need it because conformance and override checking should be sensitive to whether the conformed-to protocol/base class was imported with @preconcurrency or not, although this change is a pure refactoring.
When the conformance checker and override checker detect a difference in a function type’s @sendable attribute that varies in an illegal way, they now check if the protocol/base class was imported with an @preconcurrency import, and either limit the diagnostic or suggest adding @preconcurrency to the import as appropriate. Completes rdar://91109455.
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@swift-ci test |
DougGregor
approved these changes
Apr 9, 2022
AnthonyLatsis
added
🍒 release cherry pick
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Cherry-picks two related PRs from main to release/5.7.
#42194:
#42255: