highlight.js: (swift) does not recognize core Apple foundational libraries

I found this while writing this on Stack Overflow. I’m not sure what the root of the problem is, but I’m guessing it starts in the function signature. Here’s the code:

func configuredGridCell() -> UICollectionView.CellRegistration<UICollectionViewCell, Emoji> {
    return UICollectionView.CellRegistration<UICollectionViewCell, Emoji> { (cell, indexPath, emoji) in
        var content = UIListContentConfiguration.cell()
        content.text = emoji.text
        content.textProperties.font = .boldSystemFont(ofSize: 38)
        content.textProperties.alignment = .center
        content.directionalLayoutMargins = .zero
        cell.contentConfiguration = content
        var background = UIBackgroundConfiguration.listPlainCell()
        background.cornerRadius = 8
        background.strokeColor = .systemGray3
        background.strokeWidth = 1.0 / cell.traitCollection.displayScale
        cell.backgroundConfiguration = background
    }
}