I don't think this is true. I successfully patch TabView's underlying NSTabView on macOS 15.

Thanks for letting me know. I'll look into it.

@thcyron hmm doesn't seem to work for me. Do you have a repro I could use? I'm running the latest macOS (15.6). The closest thing to a NSTabView the view graph inspector shows is a NSToolBarView but that's a private class of no real usefulness to anyone outside Apple.

@davdroman Wrap TabView in a GroupBox, then it's a NSTabView.

Ok that does work. The GroupBox thing is a significant caveat, so I think in order to avoid confusion I'll create a separate type for it altogether... something like .tabView(placement: .groupBox) and keep the unavailable message in .tabView to let users know about this.

To your knowledge, is there any other container view capable of this transformation other than GroupBox?

Minimal example extracted from my app. Here, the ZStack seems to be key to force the TabView to not be part of the toolbar.

struct MainView: View {
    @ViewBuilder
    private var tabView: some View {
        TabView {
            Text("A")
            Text("B")
        }
        .introspect(.tabView, on: .macOS(.v15)) {
            $0.tabViewType = .noTabsNoBorder
        }
    }

    var body: some View {
        NavigationSplitView {
            Text("Sidebar")
        } detail: {
            ZStack {
                tabView
            }
        }
    }
}

Ok thanks for this. I'm torn between being specific:

.tabView(placement: .groupBox)
.tabView(placement: .zStack)
// ... anything else?

or being general:

.tabView(placement: .nonRoot) // is there a better name? .container perhaps? or .detached?

As SwiftUI tends to add more and more views each year it might be a good shout to be a bit more general to cover all possible cases without having to do heavy maintenance...

While the ZStack is crucial in the example I gave to get the traditional NSTabView layout, just wrapping in a ZStack isn't enough in all cases. If you drop the split view but keep the ZStack, you get the toolbar tab view layout again without a NSTabView.

var body: some View {
    ZStack {
        tabView
            .introspect(.tabView, on: .macOS(.v15)) {
                // never called
                $0.tabViewType = .noTabsNoBorder
            }
    }
}

As you said, we will never fully understand when a TabView is a NSTabView and when it isn't. Thus, I would suggest to keep the pre-1.4.0 behavior: allow .introspect(.tabView, on: .macOS(.v15)) and make it best-effort. If there is a NSTabView, you get it, but there isn't, you don't.

Makes sense. PR is up now btw #477