The Foundation overlay is a bit of a conundrum to work with at present:
The Xcode project cannot be compiled, at least if one adheres to the instructions, because it requires the use of the default toolchain (due to SR-12177) but also cannot be compiled with the default toolchain, since
String.swift uses the
@_spi feature to call
String(_cocoaString:) and compiling with the default toolchain does not expose the required API.
At the same time, swift-ci doesn't seem to be running the Foundation overlay tests when testing PRs in swift-corelibs-foundation on the macOS platform. I noted this when a bug correctly caused the Linux tests to fail, but the macOS test was green despite the same issue being present in both the overlay and swift-corelibs-foundation. Digging through the log, I could see no evidence of any Foundation tests being run on macOS.
How are other folks testing the overlay, and am I incorrect that swift-ci doesn't seem to be actually doing any testing of Foundation on macOS despite initial appearances?