Swift chooses sync main unless @available(macOS 12, *) added

I barely understand what is going on here, so maybe this correct behavior, but it feels pretty terrible.

I’m working on a little command line tool that doesn’t generally require macOS. Using ArgumentParser. It does do a lot of networking calls, so it uses the AsyncParsableCommand variant, an example of which looks like this:

@available(macOS 12, *)
struct CountLines: AsyncParsableCommand {
    static func main() async throws {

This didn’t work for me, but I didn’t include the @available(macOS 12, *) line. I’m told that Swift was incorrectly choosing the synchronous run() variant inherited from ParsableCommand. Somehow, with the addition of @available(macOS 12, *), it chooses the async variant I provide.

This feels pretty obscure to me, and I also dislike it because do I now have to add availability declarations for every conceivable platform? I can’t even find a list of defined platform strings for @available.

1 Like