sticky.swift

class FlippedClipView: NSClipView {
    var stickyView: NSView?
    var trailingConstraint: NSLayoutConstraint?
    
    override var isFlipped: Bool { true }
    override func layout() {
        super.layout()
        if trailingConstraint == nil, let scrollView = enclosingScrollView, let stickyView = stickyView {
            trailingConstraint = stickyView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: 0)
            trailingConstraint?.isActive = true
        }
    }
    
    override var documentRect: NSRect {
        let rect = super.documentRect
        trailingConstraint?.constant = bounds.origin.x
        return rect
    }
}