macos - iOS Xcode 12.0 Swift 5 'AppDelegate' is annotated with @main and must provide a main static function of type () -> Void or () throws -> Void

Question

In my Xcode 12.0 using Swift 5 and Catalina 10.15.5: When I tick Mac as deployable target (Apple Project Catalyst), and click Runs, it gives me an error showing:

'AppDelegate' is annotated with @main and must provide a main static function of type () -> Void or () throws -> Void.

Can't find anything on Internet... I have checked my codes and nothing's wrong and it can be run on iOS devices and simulators. Debug log is empty (duhh...)

Anyone facing this issue?

Answer 1

Change @main to @UIApplicationMain and ignore any resulting warnings.

Source: https://developer.apple.com/documentation/xcode-release-notes/xcode-12-release-notes

A newly-created iOS project using the Swift language may no longer build after enabling Mac Catalyst. (67885114)

Workaround: Replace the @main annotation on the App Delegate with @UIApplicationMain.