Support windows with native tabs

[tmandry]

These appear like separate windows in the accessibility API. Yabai doesn't support these yet so it might be difficult.

Known apps that use these:

• Alacritty
• Finder
• Ghostty
• TablePlus

[tmandry]

Did some investigation today, using Finder.

• These tabs appear as separate windows in both AX and CGWindowList APIs. Each tab has a stable ID.
• Only the current tab's objects (AX element / CG window) seem to be visible or discoverable.
  • Other tabs' elements can be used if we found them already.
• When switching between tabs we see
  • AXMainWindowChanged event to the new tab.
  • The old CG window id is replaced with the new tab's window id in the list of visible windows.
  • These events are NOT synchronized.

I don't currently have an event source for the list of visible windows changing. Maybe we can find one in the private SLS APIs.

Once we realize the windows are supposed to be the same, we can start mapping them to a consistent id. Ideally we would maintain the mapping across restarts of Glide, but that might be too ambitious to start. Maybe the right thing to do is to maintain a new mapping at the layout level or something.

Side note: If we ever get into "merging two ids known to the layout" that's a concept that is also useful for recovery.

[thomasaarholt]

I thought I'd mention that this is reported on nikitabobko/AeroSpace#68 as well.
It would be very nice to support this capability.

[MVanderloo]

Ghostty is another application that uses native tabs

[tmandry]

I thought I'd mention that this is reported on nikitabobko/AeroSpace#68 as well.

That led me to lwouis/alt-tab-macos#1540 (comment), which is a really nice investigation. That should give a way to differentiate tabs from windows.

All we would need then is an event source, maybe one of kCGSWindowDidCreate or kCGSServerWindowDidCreate from https://github.com/NUIKit/CGSInternal/blob/c4f6f559d624dc1cfc2bf24c8c19dbf653317fcf/CGSEvent.h. Would have to experiment with whether we can receive these events from sys::window_server::SkylightNotifier.

EDIT: The thread for yabai is asmvik/yabai#68

[tmandry]

Investigation notes

Detection methods:

• AX: App window list: Swapping out one window for another
  • Event: MainWindowChanged, (synthetic) WindowCreated, WindowDestroyed
  • Problem: Dependent on current space. Mitigation: Check current space before/after and bail if it changed since we last checked (also, need events on space change).
• WindowServer: Visible window list: Swapping out one window for another
  • Event: kCGSWindowIsVisible
  • Problem: Events from app actor are more authoritative, including WindowDestroyed, and there is no apparent synchronization between what the app AX server thread sees and what the window server sees. Mitigation: Make them less authoritative and rely on window server events more.
  • Benefits: Get events faster, Can get window list of particular space to remove race conditions
  • Drawback: Could break in any macOS version, requires massive refactoring (already partway done)
• Maybe something with get_windows as below: Get all windows with new first, then look for missing windows, then confirm.
  • Problem: Totally undocumented behavior. Mitigation: Can fall back to other methods.

Confirmation methods:

• Checking frequently and looking for 1:1 swap
• Checking other attributes like frame, layer match
• get_windows([a, b]) => [a], get_windows([b, a]) => [b]
  • Problem: Doesn't work when one window is destroyed. We can remember which windows are tabs but we might not have noticed the destroyed window being a tab if it wasn't created after the WM started.

Thoughts on strategy:

• Maybe it's best to do it within the app actor and rely on window server private APIs only for "enhancements", like detecting space changes earlier. This implies that we are querying the window server from different threads but I guess it's not the end of the world.
• Could give up perfect handling of destroyed tabs, and/or use a different confirmation method for them.
• Simplest thing would be to use the AX window list for create/switch/destroy, get space changed events, and bail if space is not expected or if it doesn't look like swapping exactly one window for another.