gnome: install User Themes extension

[danth]

It was always intended that Stylix would install this extension itself, as the Home Manager module's functionality relies on it.

I'm not sure whether this code has always been missing, or if it was accidentally removed at some point, as I only noticed when #1305 started happening and I went to check whether the extension was enabled.

Note that the extension is less than 100 KiB and isn't executed unless GNOME is running (it's not on $PATH or anything), so although installing this for all users is not ideal, it shouldn't cause any major problems.

Things done

• Tested locally
• Tested in testbed
• Commit message follows commit convention
• Fits style guide
• Respects license of any existing code used

Notify maintainers

[trueNAHO]

It was always intended that Stylix would install this extension itself, as the Home Manager module's functionality relies on it.

I'm not sure whether this code has always been missing, or if it was accidentally removed at some point, as I only noticed when #1305 started happening and I went to check whether the extension was enabled.

LGTM.

Note that the extension is less than 100 KiB and isn't executed unless GNOME is running (it's not on $PATH or anything), so although installing this for all users is not ideal, it shouldn't cause any major problems.

I assume some this would not be our first module to include potentially unnecessary dependencies. I suggest leaving these "performance" cleanups for the future.

[stylix-automation]

Backport failed for release-24.11, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin release-24.11
git worktree add -d .worktree/backport-1306-to-release-24.11 origin/release-24.11
cd .worktree/backport-1306-to-release-24.11
git switch --create backport-1306-to-release-24.11
git cherry-pick -x 2eaa338eb879b8432f7e252d6ab8725ada98f52d

[alyraffauf]

FYI, this is causing build errors on nix-darwin with the hm module. pkgs.gnomeExtensions.user-themes is not available on darwin.

[danth]

We should make the GNOME module only enabled by default on Linux

[0xda157]

We should make the GNOME module only enabled by default on Linux

do we ever want GNOME on darwin? if we change the default con that causes issues with #1244, if we add isLinux to config = mkIf then we won't have that issue with the docs.

[danth]

I doubt the target is useful there as it only themes GNOME Shell (so not anything you would actually have installed on MacOS)