Use of `Mutex` within the stdlib's `Concurrency` module

[Alejandro (Alejandro Alonso)]

@jamieQ

thank you for pointing this out! is the idea that API in the Synchronization module could be updated to use the StdlibDeploymentTarget availability rather than the SwiftStdlib one it currently uses, and could then be (conditionally) referenced within, say, the implementation of the Concurrency module?

assuming that's roughly in the right direction, i've tried changing a number of the Synchronization APIs to use that new availability macro (some, but not all of them in the module). doing so allows me to successfully build the stdlib target (on macOS 15), but the unit tests still seem to fail with the cannot find 'Mutex' in scope error. so the overall behavior seems unchanged, regardless of which availability macro is used.

Yeah, as a quick solution I think adopting StdlibDeploymentTarget is fine, but ideally in the near future I would like to bump the minimum deployment target of the stdlib so that the use of this macro won't be needed for types like Atomic and Mutex.

As to why you're seeing this particular error, it's because the concurrency module does not currently depend on the Synchronization module in the build system. We will need to do this eventually. cc @etcwilde we will need to make the Synchronization module a core module and not a supplementary one very soon to adopt things like Atomic and Mutex in the concurrency sources.