Include ext-foreign-toplvel-list identifiers in GET_TREE output

[tmccombs]

This would allow doing things like selecting a toplevel using a dmenu-like selector, then passing it to another process to do something with that window, such as passing it grim to take a screenshot of a window, or using it as a chooser for xdg-desktop-portal-wlr for screencasting (see emersion/xdg-desktop-portal-wlr#107 (comment)).

[emersion]

Hm, not sure I'm following. Why not grab the toplevel list via the Wayland protocol rather than the Sway IPC? That way it's not specific to Sway?

[tmccombs]

A couple of reasons.

First of all, getting a list of windows from a wayland protocol is out of scope for a program like bemenu or tofi, so being able to get this info from swaymsg would be convenient. Although, I suppose you could create a separate program for this.

Another reason is that the sway ipc provides more information than the toplevel protocol. So, for example if I wanted to use something like slurp to select a window, I could get a point from slurp, then look up which view that point is, using the geometry information from the sway ipc, then pass the foreign toplevel identifier to a screenshot or screencast tool. In some cases you might be able to associate the view with a toplevel identifier based on the app_id and title, but what if those aren't unique?

[emersion]

For the first use-caae there is e.g. https://git.sr.ht/~leon_plickat/lswt

For the second use-case that sounds like a good idea but note that with this method users won't be able to select windows on other workspaces or otherwise hidden.