@swift-5.5.3 -Xfrontend -parse-as-library @swift-5.6.3 -Xfrontend -parse-as-library @swift-main -Xfrontend -parse-as-library

import Foundation @main struct Entrypoint { static func main() async throws { print("in main():", Thread.current, Thread.isMainThread) await MainActor.run { print("in MainActor.run:", Thread.current, Thread.isMainThread) } } }

(edited)