Core Text produces glyph run with negative width for U+2028 (line separator) character when using system font with large sizes

Number:rdar://34184703 Date Originated:August 31 2017
Status: Resolved:
Product:iOS + SDK Product Version:iOS 11
Classification:Other bug Reproducible:Always
Core Graphics

As the repro code below demonstrates, Core Text produces a glyph run with negative typographic width for the Unicode character U+2028 when set with the system font on iOS in larger point sizes.

Steps to Reproduce:
Run the following code in an Xcode 9 iOS Swift playground:

import UIKit
import CoreText
let string = NSAttributedString(string: "\u{2028}",
                                attributes: [.font: UIFont.systemFont(ofSize: 40)])
let line = CTLineCreateWithAttributedString(string)
print(CTLineGetTypographicBounds(line, nil, nil, nil))

Expected Results:
The code should print a non-negative number.

Observed Results:
The code prints the negative number -0.48

iOS 11


Apple Developer Relations, November 10 2017:

A solution is under investigation. We will follow up with you again when it is available.

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