[SR-11073] Generic subclass does not respond to selector if conforming Objective-C protocol

[swift-ci]

Previous ID	SR-11073
Radar	None
Original Reporter	andoku901 (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Attachment: Download

Environment

XCode 10.2.1 default toolchain

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: 6d8b5869344f293ba1395c7797c79f52

duplicates:

• [SR-10257] Inference of @objc from witnessed protocol requirement fails sometimes #52657

Issue Description:

Write the following code in a Swift file:

class SwiftVC<View: UIView>: UIViewController, UICollectionViewDelegateFlowLayout {
    var rootView: View? {
        return self.view as? View
    }
}

final class SubSwiftVC: SwiftVC<UIView> {
    func collectionView(_ collectionView: UICollectionView,
                        layout collectionViewLayout: UICollectionViewLayout,
                        sizeForItemAt indexPath: IndexPath) -> CGSize
    {
        return .zero
    }
}

class SwiftVCAdaptor: NSObject {
    @objc func vc() -> UIViewController {
        return SubSwiftVC()
    }
}

Then write in an Objective-C file the next:

    UIViewController *vc = [[SwiftVCAdaptor new] vc];
    if ([vc respondsToSelector:@selector(collectionView:layout:sizeForItemAtIndexPath:)]) {
        // This is not executed.
    }

This behavior can be fixed by declaring collectionView:layout:sizeForItemAt: method in SwiftVC and overriding it in SubSwiftVC.