Debug UIWindow with version label above EVERYTHING

Debug+VersionInfo.swift

import UIKit

class Debug {
    static var window: UIWindow?

    static func setupWindowIfNeeded() {
        guard Debug.window == nil else { return }
        guard Environment.current != .release else { return }

        let window = UIWindow(frame: UIScreen.main.bounds)
        window.backgroundColor = .clear
        #if swift(>=4.2)
        window.windowLevel = UIWindow.Level.alert + 1
        #else
        window.windowLevel = UIWindowLevelAlert + 1
        #endif
        window.isUserInteractionEnabled = false
        window.clipsToBounds = false

        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.text = Environment.current.versionInfo
        label.font = UIFont.systemFont(ofSize: 8)
        label.textColor = UIColor.lightGray
        label.shadowColor = UIColor.darkGray
        label.textAlignment = .right

        let dummy = UIViewController()
        dummy.view.backgroundColor = UIColor.clear
        window.rootViewController = dummy

        dummy.view.addSubview(label)
        label.rightAnchor.constraint(equalTo: dummy.view.rightAnchor).isActive = true
        label.leftAnchor.constraint(equalTo: dummy.view.leftAnchor).isActive = true
        label.bottomAnchor.constraint(equalTo: dummy.view.bottomAnchor, constant: -1).isActive = true
        label.heightAnchor.constraint(equalToConstant: 12).isActive = true
        #if swift(>=4.2)
        dummy.view.bringSubviewToFront(label)
        #else
        dummy.view.bringSubview(toFront: label)
        #endif

        window.isHidden = false
        Debug.window = window
    }
}