A playground demonstrating an issue with UILabel's intrinsic content size

Playground.swift

//: Playground - noun: a place where people can play

import UIKit
import PlaygroundSupport

class LabelView: UIView {

    let label = UILabel()

    override init(frame: CGRect) {

        super.init(frame: frame)

        self.setup()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    private func setup() {

        self.label.textColor = .black
        self.label.backgroundColor = .green
        self.backgroundColor = .red
        self.label.numberOfLines = 0
        self.addSubview(self.label)

        self.label.translatesAutoresizingMaskIntoConstraints = false
        self.label.leadingAnchor.constraint(equalTo: self.leadingAnchor).isActive = true
        self.label.trailingAnchor.constraint(lessThanOrEqualTo: self.trailingAnchor).isActive = true
        self.label.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
        self.label.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
    }

    override var intrinsicContentSize: CGSize {

        let size = self.label.intrinsicContentSize

        print(size)

        return size
    }
}


class CustomView: UIView {

    let container = UIView()
    let leftLabel = LabelView()
    let rightLabel = LabelView()

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override init(frame: CGRect) {

        super.init(frame: frame)

        self.setUp()
    }

    private func setUp() {

        self.backgroundColor = .white

        self.container.backgroundColor = .gray
        self.addSubview(self.container)

        self.leftLabel.label.text = "Hello"
        self.container.addSubview(self.leftLabel)

        self.rightLabel.label.text = "Hello"
        self.rightLabel.backgroundColor = .purple
        self.container.addSubview(self.rightLabel)

        self.container.translatesAutoresizingMaskIntoConstraints = false
        self.container.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        self.container.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
        self.container.widthAnchor.constraint(equalTo: self.widthAnchor, constant: -20).isActive = true

        self.leftLabel.translatesAutoresizingMaskIntoConstraints = false
        self.leftLabel.leftAnchor.constraint(equalTo: self.container.leftAnchor, constant: 10).isActive = true
        self.leftLabel.topAnchor.constraint(greaterThanOrEqualTo: self.container.topAnchor, constant: 10).isActive = true
        self.leftLabel.bottomAnchor.constraint(lessThanOrEqualTo: self.container.bottomAnchor, constant: -10).isActive = true

        self.rightLabel.translatesAutoresizingMaskIntoConstraints = false
        self.rightLabel.rightAnchor.constraint(equalTo: self.container.rightAnchor, constant: -10).isActive = true
        self.rightLabel.topAnchor.constraint(greaterThanOrEqualTo: self.container.topAnchor, constant: 10).isActive = true
        self.rightLabel.bottomAnchor.constraint(lessThanOrEqualTo: self.container.bottomAnchor, constant: -10).isActive = true

        self.leftLabel.rightAnchor.constraint(equalTo: self.rightLabel.leftAnchor, constant: -10).isActive = true

        #if xcode8

            // Allow the left size to grow with a low hugging priority
            self.leftLabel.setContentHuggingPriority(UILayoutPriorityDefaultLow, for: .horizontal)
            // Require the right size to be no bigger than its intrinsic content size
            self.rightLabel.setContentHuggingPriority(UILayoutPriorityRequired, for: .horizontal)
            // Allow the left side to be compressed smaller than its intrinsic content size
            self.leftLabel.setContentCompressionResistancePriority(UILayoutPriorityDefaultHigh, for: .horizontal)
            // Require the right side to be no smaller than its intrinsic content size
            self.rightLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, for: .horizontal)
        #else

            // Allow the left size to grow with a low hugging priority
            self.leftLabel.setContentHuggingPriority(.defaultLow, for: .horizontal)
            // Require the right size to be no bigger than its intrinsic content size
            self.rightLabel.setContentHuggingPriority(.required, for: .horizontal)
            // Allow the left side to be compressed smaller than its intrinsic content size
            self.leftLabel.setContentCompressionResistancePriority(.defaultHigh, for: .horizontal)
            // Require the right side to be no smaller than its intrinsic content size
            self.rightLabel.setContentCompressionResistancePriority(.required, for: .horizontal)
        #endif
    }
}

class ViewController: UIViewController {

    let customView = CustomView()

    override func loadView() {

        self.view = self.customView
    }

    override func viewDidLoad() {

        super.viewDidLoad()
    }
}

print(UIDevice.current.systemVersion)

let controller = ViewController()
PlaygroundPage.current.liveView = UINavigationController(rootViewController: controller)