如何让CTFontCreateUIFontForLanguage支持汉字与Emoji？

涉及Apple平台CoreText框架，使用Swift 5.10开发时发现：当传入的UniChar数组包含汉字或Emoji字符时，CTFontCreateUIFontForLanguage()返回的字体无法正常获取对应字形。

我的尝试 #

我使用以下Swift脚本来调用CTFontCreateUIFontForLanguage()：

#!/usr/bin/env swift

import CoreText
import Foundation

guard let osFont = CTFontCreateUIFontForLanguage(
  .system, 14, "zh-Hant" as CFString
) else {
  print("CTFont initiation failed.")
  exit(1) // Abortion.
}

extension CTFont {
  func glyphs(for string: String) -> [CGGlyph]? {
    let arrUTF16 = Array(string.utf16)
    var glyphs = [CGGlyph](repeating: 0, count: arrUTF16.count)
    let result = CTFontGetGlyphsForCharacters(self, arrUTF16, &glyphs, arrUTF16.count)
    return result ? glyphs : nil
  }
}

let string = "這是草莓蛋糕🍓🍰。" // NOTE: Edit this line to try various parameters.
let unichars = Array(string.utf16)

var fetchedGlyphs: [CGGlyph]? = osFont.glyphs(for: string)
guard var fetchedGlyphs = fetchedGlyphs else {
  print("Screwed. I don't know why it only works with ASCII glyphs.")
  exit(1) // Abortion.
}

注意：上述创建的CTFont可替换为NSFont.systemFont(ofSize: NSFont.systemFontSize)，在Swift 5中CTFont与NSFont是免费桥接的。

问题现象 #

当传入的字符串参数包含汉字和/或Emoji字符时，(CTFont instance).glyphs(for:)方法返回nil。单独测试仅含汉字或仅含Emoji的字符串，同样会出现该问题。

内容的提问来源于stack exchange，提问作者Shiki Suen