Swift 5.10 Concurrency and XCTest

[tcldr]

OK, thank you @hborla ! I'll file those compiler bugs tomorrow,

@hborla

Dimension is has an explicit, unavailable Sendable conformance, which means it's definitely not a thread-safe type, so this is not an issue for Foundation to fix. If you want to use a non-Sendable type as a global/static variable in your code, you will need to isolated it to a global actor for safety to be proven statically, or wrap it in some kind of Sendable container type that protects access to it. If you don't want static data-race safety, you can mark it as nonisolated(unsafe) and take care at each use site to make sure you are synchronizing access to it, e.g. by using a lock or a dispatch queue.

The example of Dimension above is pretty much exactly how the documentation suggests a Dimension subclass should be created. The whole point is the conversion between the various statically declared units. Unless I'm missing something, It doesn't seem like its design fits with the new concurrency model. (Without getting Sendable conformance.)