Delegate methods in child class sometimes not called with Swift 5 compiler

EDIT: As sunshinejr pointed out here, this has been fixed and will be released together with the next Xcode/Swift version.

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I've found the issue, here's how to reproduce it.

class A: UIViewController, UIScrollViewDelegate {
    // ...does not implement 'scrollViewDidEndDecelerating'
}

class B: A {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Will not be called!
    }
}

What does work:

class A: UIViewController, UIScrollViewDelegate {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Probably empty
    }
}

class B: A {
    override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Will be called!
    }
}

The compiler seems to think that a delegate method is not implemented if the base class did not implement it. If only the child class implements it, it can't find it.

I still can't explain why this behaviour changed with Swift 5, but at least I've found a solution. Maybe someone can give further insights?

We ran into this with a UITextViewDelegate

Another workaround is to add the @objc tag to the method in the superclass