When synthesizing a declaration and inferring its availability, the synthesized attribute should factor in unavailability of the parent declarations. This recently regressed with https://github.com/apple/swift/pull/63361. However, the previous implementation did not produce correct results, either, because the logic for merging availability attributes produced a non-sensical result when both `unavailable` and `introduced:` availability attributes were merged. For example, this was the result for the synthesized `unownedExecutor` property of an actor when the actor was marked unavailable:
```
@available(macOS, unavailable)
actor A {
// Incorrectly synthesized availability for `unownedExecutor` which results from merging
// the unavailability of the parent and the availability of the UnownedSerialExecutor type.
@available(macOS, unavailable, introduced: macOS 10.15)
@_semantics("defaultActor") nonisolated final var unownedExecutor: UnownedSerialExecutor { get }
}
```
This is fixed by omitting all version components from the synthesized attribute when the overall attribute kind is "unavailable".
Additionally, I discovered that the `concurrency_availability.swift` test case was no longer testing what it intended to test. The conformances to `Actor` for each `actor` in the test were no longer being synthesized and therefore `unownedExecutor` was not being synthesized. That was fixed by importing the `_Concurrency` module directly, which seems to be necessary because of the `-parse-stdlib` flag in the test.
Resolves rdar://106055566
The `getInnermostDeclWithAvailability()` utility was not looking through extensions to the nominal type declaration when searching for enclosing availability.
Resolves rdar://104931478
Rather that copying availability directly from `UnownedExecutorRef`, we need
to properly infer availability from both it and the enclosing context.
Otherwise, the synthesized `unownedExecutor` will have an availability that
could conflict with our enclosing declaration.
Fixes rdar://83246377.
Remove the option that explicitly enables concurrency back-deployment,
and instead always enable its support in the compiler. Remove the use
of the extraneous CMake option as well.
When build-script is given `--back-deploy-concurrency`, also use that
to build other parts of Swift with the back-deployed versions:
* The compiler allows async and actors to be defined with the
back-deployed availability, e.g., the same as `-Xfrontend
-enable-experimental-back-deploy-concurrency`. (The latter will go
away soon)
* The standard library unit testing framework and distributed actors
library are build with the older OS versions.
* The tests use the older OS versions, with some adjustments to make
them agnostic to the back-deployment setting.
Prior versions of the _Concurrency library failed to provide
appropriate availability annotations for
`swift_deletedAsyncMethodError`, which makes them unusable with newer
Swift compilers. Avoid this problem by not checking availability for
this specific API.
Fixes rdar://80967376.
