Downgrade a mismatch on `any Sendable` -> `Any` to a warning until
Swift 6 to enable class authors to introduce concurrency annotations
to overridable properties.
Resolves: rdar://122193606
When diagnosing a case where an actor-isolated witness cannot satisfy
a non-isolated requirement, also suggest that the conformance could be
annotated with `@preconcurrency`.
Swift 5 mode.
When you annotate a ValueDecl with `@preconcurrency`, the compiler should allow
concurrency violations by downgrading errors in the actor isolation checker to
warnings in Swift 5 mode. Previously, the actor isolation checker only checked
whether the caller's context was preconcurrency when deciding to downgrade, so
referencing preconcurrency declarations directly remained errors. Preconcurrency
was also dropped when computing actor isolation for declarations imported from
clang, which are always preconcurrency.
This means that:
1. In test cases where minimal is the default (swift 5 without
-warn-concurrency), I added RUN lines for targeted, complete, and complete +
sns.
2. In test cases where complete is the default (swift 6, -warn-concurrency,
specified complete with -strict-concurrency), I added a send non-sendable run
line.
In each of these cases, I added additional expected-* lines as appropriate so
the tests can compile in each mode successfully.
It's ok to drop the global-actor qualifier `@G` from a function's type if:
- the cast is happening in a context isolated to global-actor `G`
- the function value will not be `@Sendable`
- the function value is not `async`
It's primarily safe to drop the attribute because we're already in the
same isolation domain. So it's OK to simply drop the global-actor
if we prevent the value from later leaving that isolation domain.
This means we no longer need to warn about code like this:
```
@MainActor func doIt(_ x: [Int], _ f: @MainActor (Int) -> ()) {
x.forEach(f)
// warning: converting function value of type '@MainActor (Int) -> ()' to '(Int) throws -> Void' loses global actor 'MainActor'
}
```
NOTE: this implementation is a bit gross in that the constraint solver
might emit false warnings about casts it introduced that are actually
safe. This is mainly because closure isolation is only fully determined
after constraint solving. See the FIXME's for more details.
resolves rdar://94462333
Rather than only setting the isolated-by-preconcurrency bit during
constraint application, track the closures it will be set for as part
of the constraint system and solution. Then, use that bit when
performing "strict concurrency context" checks and type adjustments,
so we don't treat an inferred-to-by-`@Sendable`-by-preconcurrency
closure in the solver as if it weren't related to preconcurrency.
Fixes the spurious warning from
https://github.com/apple/swift/issues/59910.
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>.
Introduce the `@preconcurrency` attribute name for `@_predatesConcurrency`,
which has been the favored name in the pitch thread so far. Retain the
old name for now to help smooth migration.
The main effect of this change is that diagnostics about Sendable
conformances now follow the same minimal/full logic used for other
Sendable diagnostics, rather than having their own separate
computation.
These have been subsumed by @_predatesConcurrency. Leave in minimal
parser support that warns about the removal, so we don't fully break
existing source code.
When the Error and CodingKey protocols introduced their Sendable
requirements, we carved out special Sendable checking rules that
suppressed diagnostics when a type becaming Sendable implicitly via
conformance to Error or CodingKey. Extend that logic to any protocol
that predates concurrency, so that existing libraries can benefit from
the same staging we used for Error and CodingKey.
In the future, we can mark Error and CodingKey to eliminate the
special case.
Introduce the `@_predatesConcurrency` attribute, which specifies that a
given declaration existed prior to the introduction of Swift
Concurrency, has been updated to use concurrency features (global
actors, Sendable, etc.), but should retain its pre-concurrency behavior
for clients that have not yet opted into concurrency.
Implement type and actor-isolation adjustments to
`@_predatesConcurrency` declarations to subsume the `@_unsafeMainActor`,
`@_unsafeSendable`, and `@MainActor(unsafe)` use cases. This is the
bulk of the semantic transformations needed for this new attribute,
but is not yet complete.
Part of rdar://84448438.
