libnyanpasu/clash-nyanpasu · warning · anyhow::Error

failed to get title bar container view

Error message

failed to get title bar container view

What it means

After obtaining the close button, set_traffic_lights_pos navigates two superview levels up to reach AppKit's private title bar container view (NSTitlebarContainerView). If either superview is nil, the code fails with this error. The title bar container is an undocumented view hierarchy detail, so this breaks when AppKit changes the hierarchy or the window is styled differently.

Source

Thrown at backend/tauri/src/window.rs:925

        pos: Position,
    ) -> anyhow::Result<()> {
        use objc2_app_kit::NSWindowButton;
        use objc2_foundation::NSRect;
        let close = window
            .standardWindowButton(NSWindowButton::CloseButton)
            .ok_or(anyhow::anyhow!("failed to get close button"))?;
        let miniaturize = window
            .standardWindowButton(NSWindowButton::MiniaturizeButton)
            .ok_or(anyhow::anyhow!("failed to get miniaturize button"))?;
        let zoom = window
            .standardWindowButton(NSWindowButton::ZoomButton)
            .ok_or(anyhow::anyhow!("failed to get zoom button"))?;

        let title_bar_container_view = unsafe {
            close
                .superview()
                .and_then(|view| view.superview())
                .ok_or(anyhow::anyhow!("failed to get title bar container view"))?
        };

        let close_rect = close.frame();
        let button_height = close_rect.size.height;

        let title_bar_frame_height = button_height + pos.y;
        let mut title_bar_rect = title_bar_container_view.frame();
        title_bar_rect.size.height = title_bar_frame_height;
        title_bar_rect.origin.y = window.frame().size.height - title_bar_frame_height;
        unsafe {
            title_bar_container_view.setFrame(title_bar_rect);
        }

        let space_between = miniaturize.frame().origin.x - close.frame().origin.x;
        let window_buttons = vec![close, miniaturize, zoom];

        for (i, button) in window_buttons.into_iter().enumerate() {
            let mut rect: NSRect = button.frame();

View on GitHub (pinned to f7dbce2997)

Solutions

1. Walk the superview chain searching for the NSTitlebarContainerView class instead of assuming a fixed two-level depth
2. Guard with respondsToSelector/class checks and skip repositioning gracefully on hierarchy mismatch
3. Pin behavior per macOS version and test on each supported release after upgrades
4. If the hierarchy lookup fails, fall back to not adjusting traffic lights (log a warning)

Example fix

// before
let title_bar_container_view = unsafe {
    close.superview().and_then(|view| view.superview())
        .ok_or(anyhow::anyhow!("failed to get title bar container view"))?
};
// after
let title_bar_container_view = unsafe {
    let mut v = close.superview();
    while let Some(view) = v {
        if view.is_kind_of::<objc2_app_kit::NSTitlebarContainerView>() { break; }
        v = view.superview();
    }
    v.ok_or_else(|| anyhow::anyhow!("NSTitlebarContainerView not found in superview chain"))?
};

// verify the expected superview depth before casting
let container = close.superview().and_then(|v| v.superview());
if container.is_none() {
    return Ok(()); // hierarchy not as expected
}

fn is_titlebar_container(view: &objc2_runtime::AnyObject) -> bool {
    unsafe { view.is_kind_of::<objc2_app_kit::NSTitlebarContainerView>() }
}

if let Err(e) = set_traffic_lights_pos(window, pos) {
    log::warn!("traffic light positioning unavailable (AppKit hierarchy changed?): {e}");
}

When it happens

Trigger: set_traffic_lights_pos called on a window whose close button has no two-level superview chain — undecorated/overlay title bars, macOS versions where NSTitlebarContainerView is absent (no titlebar), or bridged views from a non-standard window setup.

Common situations: macOS version upgrades changing the private view hierarchy; Tauri titleBarStyle overlay windows; windows in fullscreen where the titlebar container is detached; very new macOS releases where the private class layout differs.

Related errors

• failed to get close button
• failed to get miniaturize button
• failed to get zoom button
• failed to get title bar container view
• failed to get close button

AI-assisted analysis of libnyanpasu/clash-nyanpasu@f7dbce2997 (2026-09-08). Data as JSON: /api/errors/06303f2be5df2f5d. Report an issue: GitHub.