GTK/Qt theme not working

[musjj]

Describe the bug

I've followed the instructions described in the manual, but Qt applications are not using my GTK theme.

Steps To Reproduce

qt.enable = true;
qt.platformTheme = "gtk2";
qt.style = "gtk2";
environment.systemPackages = [ pkgs.qalculate-qt ];

Running qalculate-qt will yield the following error:

QApplication: invalid style override 'gtk2' passed, ignoring it.
	Available styles: Windows, Fusion

Expected behavior

Qt applications should properly detect the gtk2 style.

Notify maintainers

@romildo

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.1.39, NixOS, 23.11 (Tapir), 23.11.20230721.9ca7856`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.15.1`
 - nixpkgs: `/nix/store/d1fspdh09fpk7dkl5s667vhpkgv12dsx-source`

[bobby285271]

Yeah qalculate-qt (and anki) are Qt 6 applications, I expect the gtk2 style not working before someone package https://github.com/trialuser02/qt6gtk2 (theming for Qt 5 should work since we have https://github.com/qt/qtstyleplugins though 🙃)

[Misterio77]

Here's qt6gtk2: #245571

With that PR merged, this issue should be fixed right out of the box when using NixOS to manage qt.

[musjj]

Thank you for the PR!