Window activation support

[kchibisov]

On Wayland for link to raise window(e.g. when clicking a link in application, the launcher application should be opened with some env variable set to specific token).

Both X11 and Wayland has concept like that, see

https://wayland.app/protocols/xdg-activation-v1 and its XDG_ACTIVATION_TOKEN variable.

And X11
https://cgit.freedesktop.org/startup-notification/tree/doc/startup-notification.txt

I'm not sure whether macOS or Windows have something like that, but they probably should.

For now, to account for Wayland, we should add a method on WindowBuilder::with_activation_token(<Option<String>>) and add a method on a particular window to request activation token.

The first will be used when the application is raised from other process or in multiwindow context. The later to run launchers e.g. xdg-open or same in multiwindow context.

cc @ArturKovacs @maroider @madsmtm

--

I'll send Wayland impl and impl it in alacritty, since it looks pretty straightforward.

[kchibisov]

I was a bit wrong wrt API, given that Wayland is async here and you must creating a token is a request to compositor leaving you wait until the request is done means that it should reply to application async via some event...

[madsmtm]

Not sure I understand, is the "activation token" equivalent to an "application id" (macOS has those)? If no, how do they differ? Would this allow a similar thing as #1751?

[kchibisov]

No, it's completely different thing. It's basically what Window::focus_window does. And if you pass it to a launcher, launched window can read this token and request focus.

Example, clicking on links in terminal will switch focus to a browser or mark it as urgent(depends on compositor). Without token passing it's impossible to know where the link opened or what actually launched.

It could be passed to other winit window, so it'll get focus or if you want to switch focus to other winit window when feel like.