Newline has wrong appearance when line spacing used

[romanr]

SwiftUI wrapper via STTextViewSwiftUI.TextView

• Line spacing applied via NSParagraphStyle.lineSpacing in every NSAttributedString set on the view
• TypingStylePlugin (STPlugin) sets textView.defaultParagraphStyle with the same lineSpacing so new empty paragraphs inherit it

Can't get it working, do I understand correctly that this it TextKit 2 / NSTextLayoutManager bug?
what is the workaround?
Like an NSTextLayoutManagerDelegate method, NSTextLayoutFragment override? or other TextKit 2 API to correct typographicBounds for empty paragraph line fragments so they report content height only (not content + lineSpacing)?

with line height and line spacing:

when Enter or \n is entered new line is like double height with no line spacing before it:

---

as soon as any letter is typed, it's normal as expected:

[krzyzanowskim]

is it reproducible in non SwiftUI? haven't seen that one

[romanr]

this is Playground code

import AppKit

// Reproduces TextKit 2 bug: empty paragraph line fragments have
// typographicBounds.height ≈ (contentHeight + lineSpacing) instead of contentHeight only.
//
// Pure TextKit 2 stack — no STTextView, no SwiftUI, no NSTextView.

let font = NSFont.monospacedSystemFont(ofSize: 14, weight: .regular)
let lineSpacing = font.ascender - font.descender + font.leading

print("Font: ascender=\(font.ascender) descender=\(font.descender) leading=\(font.leading)")
print("lineSpacing=\(lineSpacing)  naturalHeight=\(font.ascender - font.descender)")

let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineSpacing = lineSpacing

let attrString = NSAttributedString(
    string: "Roses are red\nViolets are blue\n\n",
    attributes: [.font: font, .paragraphStyle: paragraphStyle]
)

let contentStorage = NSTextContentStorage()
let layoutManager  = NSTextLayoutManager()
let container      = NSTextContainer(size: CGSize(width: 400, height: CGFloat.greatestFiniteMagnitude))
layoutManager.textContainer = container
contentStorage.addTextLayoutManager(layoutManager)

contentStorage.performEditingTransaction {
    contentStorage.attributedString = attrString
}

// nil start = beginning of document; .ensuresLayout forces layout on demand
var i = 0
layoutManager.enumerateTextLayoutFragments(
    from: nil,
    options: [.ensuresLayout, .ensuresExtraLineFragment]
) { frag in
    let f = frag.layoutFragmentFrame
    print("\nFragment[\(i)] y=\(String(format:"%.3f",f.origin.y)) h=\(String(format:"%.3f",f.height))")
    i += 1
    for (j, line) in frag.textLineFragments.enumerated() {
        let h      = line.typographicBounds.height
        let str    = (line.attributedString.string as NSString).substring(with: line.characterRange)
        let label  = str.replacingOccurrences(of: "\n", with: "\\n")
        print("  Line[\(j)] typoBounds.h=\(String(format:"%.3f",h))  \"\(label)\"")
    }
    return true
}

[krzyzanowskim]

all we need is new TextKit2 bug to workaround

[romanr]

you think it's a textKit2 bug?