Some more `qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.` errors

[piegamesde]

Describe the bug

Some QT applications (I only tested Kile, but it's probably some more) are broken on latest master.

To Reproduce Steps to reproduce the behavior:

NIX_PATH=nixpkgs=https://github.com/nixos/nixpkgs/archive/90321a7bb31f129ce6b0594fa5614c7a83c72528.tar.gz nixGLIntel nix-shell -p 'kile' --pure --run kile

Error message:

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Additional context

This is similar to #99937. Also some of the discussion in #99956

Notify maintainers

@FRidh

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

• system: "x86_64-linux"
• host os: Linux 5.8.10-arch1-1, Arch Linux, noversion
• multi-user?: no
• sandbox: yes
• version: nix-env (Nix) 2.3.7
• channels(user): "home-manager, nixpkgs-21.03pre244772.502845c3e31"
• nixpkgs: ~/.nix-defexpr/channels/nixpkgs

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:

[FRidh]

fixed on master with c5a41da563485db7e34475321e22d45941de23d0 and on release-20.09 with 5f9c8a1976b63fb31d280f9d9fef3c0e678d0bec.

I did notice the theme was not OK for me on master, so we may need to downgrade to Qt 5.12 there as well. Let me know if there are any more issues!

[piegamesde]

Thanks for the quick fix.