Some mixed-language projects import Objective-C headers through their umbrella or bridging header that declare things that are actually implemented in Swift. This isn’t something we really supported or had tests for, but it happens in practice and we can’t break them.
Carve out a second exception to method conflict checking for when all of the conflicting methods are imported ObjC methods in either the same module or a bridging header.
Fixes rdar://96470068.
`@Sendable` on completion handlers imported from Objective-C has been
implemented for a while, but has been disabled in production builds
due to a number of problems we've encountered with rolling it out.
Introduce an experimental feature for `@Sendable` completion handlers
so we can iterate on this more before we enable it by default.
Part of rdar://85569247, which will cover re-landing this feature.
The change in #59479 inadvertently fixed another bug in selector conflict checking: Swift did not notice when an ObjC header declared an async-imported method, but a Swift extension to the same class added another method with the same selector. Unfortunately, fixing this bug was source-breaking, and it also caused Swift to diagnose spurious conflicts between the various names that a single ObjC method might be imported with. Soften the error to a warning in Swift 5 mode and suppress the spurious diagnostics.
Fixes rdar://95887113.
When a closure is not properly actor-isolated, but we know that we inferred its isolation from a `@preconcurrency` declaration, we now emit the errors as warnings in Swift 5 mode to avoid breaking source compatibility if the isolation was added retroactively.
In an async context, trying to pass a non-`@Sendable` function to an `@Sendable` parameter or trying to assign a `@MainActor` method to a non-`@MainActor`-typed variable were hard errors. We now think that this a mistake for `@preconcurrency` APIs in Swift 5 mode, as it hinders retroactive adoption of `@Sendable` and `@MainActor` by libraries.
This PR weakens these errors to warnings *only* when the decl which contains the attribute in its type signature is `@preconcurrency` and *only* when in Swift 5 mode (with or without -warn-concurrency). For non-`@preconcurrency` decls, it is still an error.
Fixes <rdar://88703266>.
