focus-follows-mouse should follow windows too

[mitchellh]

Discussed in #5383

^{Originally posted by edrozenberg January 26, 2025}
Currently focus-follows-mouse only works for focusing different splits within a single window/tab.

ghostty.org/docs/config/reference#focus-follows-mouse

For some use-cases it would be nice to be able to set focus-follows-mouse to also work between Ghostty windows, for ex. a window on the left and a window on the right.

Maybe something like:
focus-follows-mouse = < splits | windows | all | false >

There are some Mac utilities that might enable window-based focus follow for all apps, but I'd want to enable it specifically for Ghostty.

For reference, Mac's Terminal.app currently provides window-based focus follow:
defaults write com.apple.Terminal FocusFollowsMouse -bool YES

My Q is specifically about Mac but may apply to Linux also. I'm aware Linux has long had the option to enable global focus follows mouse between windows. I don't know if it's possible to control this at the app level on Linux, not educated well enough on this topic on Linux OS's.

Mitchell's Notes

I like the proposal here, I think changing it to a packed struct would yield all of these options. I think true should by default turn them all on (which you'll get for free with a packed struct).

As noted in the discussion, I'm not sure if this is even possible with GTK but if not we should just document it as a limitation.