Add support for wayland copy/paste

[SMillerDev]

Description

This PR adds support for an xclip alternative for wayland: https://github.com/bugaevc/wl-clipboard

TODOs:

• Changes to fish usage are reflected in user documentation/manpages.
• Tests have been added for regressions fixed
• User-visible changes noted in CHANGELOG.md

[faho]

What happens if you have both installed?

If you are running X, it'll pick the x thing, but what if you're running wayland?

I'm not entirely up-to-date here (every kwin release I try it to see that it still doesn't support scripts, and then I go back), is there an accepted standard for detecting wayland? E.g. some $DISPLAY alternative? Or $XDG_SESSION_TYPE? That's set to "x11" on my system.

[SMillerDev]

echo $XDG_SESSION_TYPE
wayland

I'm not sure if there's an official standard but this could work. I'd guess people with wayland would uninstall xclip though? So it would fall through to wl-*?

[mqudsi]

You could check for the X11 DISPLAY environment variable. xclip won't work without it, and it won't be set if you're using wayland. For more reliable than depending on wayland users not to have xclip installed.

[faho]

it won't be set if you're using wayland

I'm not sure on that. What about if you have xwayland? Though xclip will probably work then.

[SMillerDev]

The DISPLAY variable is set for me on Wayland. But that might be something wrong in my setup. XDG_SESSION_TYPE is able to identity Wayland though.

[faho]

The DISPLAY variable is set for me on Wayland. But that might be something wrong in my setup.

Yeah, no. XWayland is supposed to be transparent to applications, so I'm pretty sure $DISPLAY needs to be set.

[mqudsi]

I didn't consider xwayland. You can disregard my suggestion :)

[faho]

Okay, I'm merging this now, because it'll fix the case where wayland users don't have any of the X utilities, and as far as I know the X things still work on wayland via XWayland.