Qt platform plugin not found for joint-state-publisher-gui

[CTerasa]

Description

Running the humble joint_state_publisher_gui I get the following error and the GUI does not start

$ ros2 run joint_state_publisher_gui joint_state_publisher_gui 
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

[ros2run]: Aborted

Minimal flake.nix sample:

{
  inputs = {
    nix-ros-overlay.url = "github:lopsided98/nix-ros-overlay/master";
    nixpkgs.follows = "nix-ros-overlay/nixpkgs"; # IMPORTANT!!!
  };
  outputs =
    {
      self,
      nix-ros-overlay,
      nixpkgs,
    }:
    nix-ros-overlay.inputs.flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ nix-ros-overlay.overlays.default ];
        };
      in
      {
        devShells.default = pkgs.mkShell {
          name = "Minimal sample for joint-state-publisher-gui";
          packages = [
            # ... other non-ROS packages
            (
              with pkgs.rosPackages.humble;
              buildEnv {
                paths =
                  [
                    ros-core
                    joint-state-publisher-gui
                  ];
              }
            )
          ];
        };
      }
    );
}

Expected behavior

The GUI should start and the output should look similar to the following

$ ros2 run joint_state_publisher_gui joint_state_publisher_gui 
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
[INFO] [1739624382.427781012] [joint_state_publisher]: Waiting for robot_description to be published on the robot_description topic...
[INFO] [1739624382.436617151] [joint_state_publisher]: Centering

Observations and Workaround

It seems that the ros2 execution does not have the correct QT_PLUGINS_PATH environment variable set. Thus the Qt QPA plugins cannot be found.

When I search for the Qt platform plugins and set the QT_PLUGINS_PATH the joint_state_publisher_gui starts up like expected.

$ export QT_PLUGIN_PATH=$(realpath $(dirname $(ls -d /nix/store/*/lib/qt-5.15.15/plugins/platforms/*xcb*| head -n1))/..)
$ ros2 run joint_state_publisher_gui joint_state_publisher_gui

With my limited knowledge of nix and nix-ros-overlay, I could not fix this in the package on my own.

I think the same issue prevents from starting the demos and working with the Humble URDF tutorial when using the urdf-tutorial.

[wentasah]

#577 should fix this. Or you can add:

shellHook = ''
  export QT_PLUGIN_PATH=${pkgs.qt5.qtbase}/${pkgs.qt5.qtbase.qtPluginPrefix}
'';

as an argument to pkgs.mkShell.

[CTerasa]

Thank you, the shellHook you proposed works like a charm.

Thought I tried something similar as in the change #577, however I had no success. Perhaps I made some kind of mistake on the way. I can verify that using the branch from #577 it is also working.
Keeping this issue open until #577 is merged.

Thanks and great support!