Wrong error: Class property 'X' isolated to global actor 'MainActor' can not be referenced from a non-isolated synchronous context

[yyaroshevich]

Describe the bug
UIApplication.willTerminateNotification should accessible in non-isolated synchronous context

To Reproduce
Steps to reproduce the behavior:

1. Try to accessUIApplication.willTerminateNotification from an actor. Either from isolated or non isolated function

actor Test {
  nonisolated func subscribeApplicationNotifications() -> [Any] {
    let applicationWillTerminateObserver = NotificationCenter.default.addObserver(forName: UIApplication.willTerminateNotification,
                                                                          object: nil,
                                                                          queue: nil) { [weak self] notification in
      // do something
    }
    return [applicationWillTerminateObserver]
  }
}

2. Observe compilation error:

Class property 'willTerminateNotification' isolated to global actor 'MainActor' can not be referenced from a non-isolated synchronous context

or

Class property 'willTerminateNotification' isolated to global actor 'MainActor' can not be referenced from actor 'Test' in a synchronous context

Expected behavior
Code is compiled

Screenshots

Environment (please complete the following information):

• OS: MacOS 12.3.1 (21E258)
• Xcode Version 13.4 (13F17a)

Additional context
Workaround for a problem would be:

private enum Constants {
  static let uiApplicationWillTerminate = UIApplication.willTerminateNotification
}

and then reference it when necessary as Constants.uiApplicationWillTerminate

[yyaroshevich]

Workaround does not work with -warn-concurrency on XCode 14.0 / Swift 5.7

[theblixguy]

UIApplication is annotated with @MainActor so property access needs to be isolated to that.

[yyaroshevich]

But is that annotation correct? So basically it looks like access to static readonly (immutable?) member of class, which sound like safe thing to do from any thread (of course until there is no complex initializer inside with lazy initialization, but that's hard to believe for that simple property).

[theblixguy]

I am not sure, since it's a question about an Apple framework (UIKit) I'd recomend asking this question over at https://developer.apple.com/forums/ or sending a feedback via https://feedbackassistant.apple.com/

[NachoSoto]

access to static readonly (immutable?) member of class, which sound like safe thing to do from any thread

This is still an issue on Swift 5.9

Having to call NotificationCenter.addObserver (which is Sendable) on @MainActor just because UIApplication is marked with MainActor makes nos ense.

[NachoSoto]

access to static readonly (immutable?) member of class, which sound like safe thing to do from any thread

This is still an issue on Swift 5.9

Having to call NotificationCenter.addObserver (which is Sendable) on @MainActor just because UIApplication is marked with MainActor makes no sense.