AppDelegate.swift:4:1 'UIApplicationMain' is deprecated; this is an error in Swift 6

[jmagman]

In Xcode 15.3 beta I see a deprecation warning in a newly created Flutter iOS Xcode project. @UIApplicationMain was renamed to @main in Swift 5.3.

AppDelegate.swift:4:1 'UIApplicationMain' is deprecated; this is an error in Swift 6

flutter/packages/flutter_tools/templates/app_shared/ios-swift.tmpl/Runner/AppDelegate.swift

Line 4 in db141ec

@UIApplicationMain

We already require Xcode 14, and Swift 5.3 was introduced in Xcode 12.

I bet the same is needed for @NSApplicationMain but I didn't check.

flutter/packages/flutter_tools/templates/app_shared/macos.tmpl/Runner/AppDelegate.swift

Line 4 in db141ec

@NSApplicationMain

I'm not sure if there are other implications to using @main instead of @UIApplicationMain (scene delegates?)

[hellohuanlin]

From https://stackoverflow.com/questions/67429098/what-is-the-differnce-between-main-and-uiapplicationmain

Looks like for our use case they are the same (we don't have a custom main class to annotate)

[christopherfujino]

cc @eliasyishak

[loic-sharma]

I'm not sure if there are other implications to using @main instead of @UIApplicationMain (scene delegates?)

@main requires Swift 5.3, which requires Xcode 12. That seems acceptable given our docs recommend installing Xcode 15.

Also from: https://forums.swift.org/t/se-0383-deprecate-uiapplicationmain-and-nsapplicationmain/62375/9

For example, one could go out of their way to declare a static func main() {} in their app delegate that, upon migration, would get automatically called instead of the main provided by an application delegate conformance:

@main // was @UIApplicationMain
actor AppDelegate: NSObject, NSApplicationDelegate {
  static func main() {
    fatalError("oops")
  }
}

They'd need to change the name of this function in addition to adopting the @main attribute to avoid the code exploding. This example would crash on launch, and a less contrived example wouldn't call UIApplicationMain or NSApplicationMain to set anything up, so I think the authors of such an implementation would catch it pretty quickly.

If we wanted to, we could guard against this by checking if the app delegate has something that looks like static func main(). However, this doesn't seem necessary; Swift's migration doesn't bother to check this either.

More details can be found in this proposal: https://github.com/apple/swift-evolution/blob/main/proposals/0383-deprecate-uiapplicationmain-and-nsapplicationmain.md

[github-actions]

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