Include an extension for a class only if iOS11 is available

Question

I am trying to extend a class written in Obj-C and include an extension written in Swift that makes it conform to the UIDropInteractionDelegate, like so:

@available(iOS 11.0, *)
extension NoteEditViewController: UIDropInteractionDelegate {
    @available(iOS 11.0, *)
    public func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {
        let operation: UIDropOperation
        if session.localDragSession == nil {
            operation = .forbidden
        } else {
            // If a local drag session exists, we only want to move an
            // existing item in the pin board to a different location.
            operation = .forbidden
        }
        return UIDropProposal(operation: operation)
    }

    @objc(setupDropInteractions)
    @available(iOS 11.0, *)
    func setupDropInteractions() {
        // Add drop interaction
        self.view.addInteraction(UIDropInteraction(delegate: self))
    }
}

My problem is that Project_Name-Swift.h file contains the following code that will not compile:

@class UIDropInteraction;
@protocol UIDropSession;
@class UIDropProposal;

// This line is causing the issue saying "'UIDropInteractionDelegate' is partial: introduced in iOS 11.0"
@interface NoteEditViewController (SWIFT_EXTENSION(Bloomberg_Professional)) <UIDropInteractionDelegate>
- (UIDropProposal * _Nonnull)dropInteraction:(UIDropInteraction * _Nonnull)interaction sessionDidUpdate:(id <UIDropSession> _Nonnull)session SWIFT_WARN_UNUSED_RESULT SWIFT_AVAILABILITY(ios,introduced=11.0);
- (void)setupDropInteractions SWIFT_AVAILABILITY(ios,introduced=11.0);
@end

The compiler is complaining that the interface in that file is partial.

'UIDropInteractionDelegate' is partial: introduced in iOS 11.0

I assumed that including the @available(iOS 11.0, *) would generate a SWIFT_AVAILABILITY(ios,introduced=11.0) that would encapsulate the entire interface but I was wrong.

Is there a way to fix this?

UPDATE

---

I implemented a toy example.

Here is the toy ViewController:

Here is the swift extension:

And here is the generated dnd_toy-Swift.h file.

You were right that it is simply a warning but my problem is that we must treat all warnings as errors in our project.

Any ideas on how to get rid of this warning from here?

Answer 1

Xcode 9 beta 4 will build, if @available is added to each method. The build still fails if @available is added only at the extension level.