Tibetan characters cause NSLayoutManager to return incorrect bounding rect (rdar://48745247)

MyPlayground.swift

let string = "If the Tibetan characters དོམ་ཁྲ are removed, then the function boundingRect(forGlyphRange:in:) returns the correct value. Note that the values are incorrect for any range in a paragraph containing these characters."
let textStorage = NSTextStorage(string: string)
textStorage.addAttribute(.font, value: UIFont.systemFont(ofSize: UIFont.labelFontSize), range: NSRange(0 ..< textStorage.length))

// Xcode in dark mode makes the text hard to read.
textStorage.addAttribute(.foregroundColor, value: UIColor.white, range: NSRange(0 ..< textStorage.length))

let textContainer = NSTextContainer(size: CGSize(width: 300, height: 300))
let layoutManager = NSLayoutManager()
layoutManager.addTextContainer(textContainer)
textStorage.addLayoutManager(layoutManager)

let characterRange = string.range(of: "If the Tibetan characters")!
let glyphRange = layoutManager.glyphRange(forCharacterRange: NSRange(characterRange, in: string), actualCharacterRange: nil)
let boundingRect = layoutManager.boundingRect(forGlyphRange: glyphRange, in: textContainer)

let offset: CGFloat = 10
let renderer = UIGraphicsImageRenderer(size: CGSize(width: textContainer.size.width + 2 * offset, height: textContainer.size.height + 2 * offset))
let image = renderer.image { context in
    let glyphRange = NSRange(0 ..< layoutManager.numberOfGlyphs)
    let origin = CGPoint(x: offset, y: offset)
    layoutManager.drawBackground(forGlyphRange: glyphRange, at: origin)
    layoutManager.drawGlyphs(forGlyphRange: glyphRange, at: origin)

    UIColor.red.set()
    UIRectFrame(boundingRect.offsetBy(dx: offset, dy: offset))
}

Incorrect and correct bounding rects

Don't suppose you found a fix?

@dennda Unfortunately not. No reply on the bug report either :(