Workaround for rdar://42199059

Workaround42199059.swift

extension NSLayoutManager {
    func invalidateLayout() {
        let characterRange: NSRange
        if let textStorage = textStorage {
            // fast path
            characterRange = NSRange(0 ..< textStorage.length)
        } else {
            characterRange = self.characterRange(forGlyphRange: NSRange(0 ..< numberOfGlyphs), actualGlyphRange: nil)
        }

        invalidateLayout(forCharacterRange: characterRange, actualCharacterRange: nil)
    }
}

extension UIView {
    var readableContentMargins: UIEdgeInsets {
        let guide = readableContentGuide
        guard let owningView = guide.owningView else {
            return .zero
        }

        let readableFrame = guide.layoutFrame
        return UIEdgeInsets(
            top: readableFrame.minY,
            left: readableFrame.minX,
            bottom: owningView.bounds.maxY - readableFrame.maxY,
            right: owningView.bounds.maxX - readableFrame.maxX
        )
    }
}

// Called from `viewLayoutMarginsDidChange()` on iOS 11+ -- otherwise viewDidLayoutSubviews()
func updateContentInset() {
    if let textView = textView {
        let margins = view.readableContentMargins
        textView.contentInset = UIEdgeInsets(top: 0, left: margins.left, bottom: 0, right: margins.right)
        textView.layoutManager.invalidateLayout()
    }
}