qt: adds default value for qt.platform

[Mikilio]

extra additions related to d171b19.
Adds a default value so it does not fail like in issue #835

[trueNAHO]

Can you rebase this on top of master? I assume only commit 0d75bef needs to be cherry-picked.

[trueNAHO]

How does this PR compare to nix-community/home-manager#6493?

[Mikilio]

How does this PR compare to nix-community/home-manager#6493?

Unrelated I have subscribed to nix-community/home-manager#6493 and will adapt in a new PR that also fixes #869

[nixith]

Defaults are already handled for the qt nixos modules here with extra logic I believe

stylix/modules/qt/nixos.nix

Lines 40 to 49 in f121a14

	stylix.targets.qt.platform =
	with config.services.xserver.desktopManager;
	if gnome.enable && !(plasma5.enable || lxqt.enable) then
	"gnome"
	else if plasma5.enable && !(gnome.enable || lxqt.enable) then
	"kde"
	else if lxqt.enable && !(gnome.enable || plasma5.enable) then
	"lxqt"
	else
	"qtct";

Wouldn't it be better to move this block of code up, or otherwise mark this value as lib.mkDefault?

I haven't tested it yet, but as it stands I think this value will collide with what is set in the option if the two differ anyways.

[Mikilio]

lib.mkDefault is discouraged by @danth. In fact, I used it before like that.
The redundancy is true. The case where we need this is where the NixOS level home-manager integration needs to access this variable as it is shared with the home-manager configuration. This in particular also happens when plasma6 is set and the module is effectively disabled. One thing I could add is to also explicitly disable the home-manager module in this case.

Keep in mind that this only a temporary fix for like 2-3 weeks to ensure backwards compatibility and avoid build errors.
Proper CI/CD is still work in progress afaik.

[trueNAHO]

LGTM.

lib.mkDefault is discouraged by [danth].

For reference, this is explained in #388.