WindowController.swift

id.swift

fileprivate extension NSTouchBarCustomizationIdentifier {
    static let windowBar = NSTouchBarCustomizationIdentifier("com.n3tr.countertouchbar.touchbar")
}

fileprivate extension NSTouchBarItemIdentifier {
    static let label = NSTouchBarItemIdentifier("com.n3tr.countertouchbar.label")
}

class WindowController: NSWindowController {
  // ...
}

makeTouchBar.swift

class WindowController: NSWindowController {
    // ..
    override func makeTouchBar() -> NSTouchBar? {
        let touchBar = NSTouchBar()
        touchBar.delegate = self
        touchBar.customizationIdentifier = .touchBar
        touchBar.defaultItemIdentifiers = [.label]
        return touchBar
    }
}