nix-config/modules/sessions/plasma.nix

{
  flake.nixosModules.plasma = { pkgs, ... }: {
    services.desktopManager.plasma6.enable = true;
    services.displayManager.plasma-login-manager.enable = true;
    services.power-profiles-daemon.enable = false;
    services.xserver.enable = false;

    environment.systemPackages = with pkgs; [ 
      klassy 
    ];

    nixpkgs.overlays = [
      (final: prev: {
        kdePackages = prev.kdePackages.overrideScope (
          kdeFinal: kdePrev: {
            # https://old.reddit.com/r/NixOS/comments/1pdtc3v/kde_plasma_is_slow_compared_to_any_other_distro/
            # https://github.com/NixOS/nixpkgs/issues/126590#issuecomment-3194531220
            plasma-workspace =
              let
                # the package we want to override
                basePkg = kdePrev.plasma-workspace;
                # a helper package that merges all the XDG_DATA_DIRS into a single directory
                xdgdataPkg = final.stdenv.mkDerivation {
                  name = "${basePkg.name}-xdgdata";
                  buildInputs = [ basePkg ];
                  dontUnpack = true;
                  dontFixup = true;
                  dontWrapQtApps = true;
                  installPhase = ''
                    mkdir -p $out/share
                    ( IFS=:
                      for DIR in $XDG_DATA_DIRS; do
                        if [[ -d "$DIR" ]]; then
                          ${prev.lib.getExe prev.lndir} -silent "$DIR" $out
                        fi
                      done
                    )
                  '';
                };
                # undo the XDG_DATA_DIRS injection that is usually done in the qt wrapper
                # script and instead inject the path of the above helper package
                derivedPkg = basePkg.overrideAttrs {
                  preFixup = ''
                    for index in "''${!qtWrapperArgs[@]}"; do
                      if [[ ''${qtWrapperArgs[$((index+0))]} == "--prefix" ]] && [[ ''${qtWrapperArgs[$((index+1))]} == "XDG_DATA_DIRS" ]]; then
                        unset -v "qtWrapperArgs[$((index+0))]"
                        unset -v "qtWrapperArgs[$((index+1))]"
                        unset -v "qtWrapperArgs[$((index+2))]"
                        unset -v "qtWrapperArgs[$((index+3))]"
                      fi
                    done
                    qtWrapperArgs=("''${qtWrapperArgs[@]}")
                    qtWrapperArgs+=(--prefix XDG_DATA_DIRS : "${xdgdataPkg}/share")
                    qtWrapperArgs+=(--prefix XDG_DATA_DIRS : "$out/share")
                  '';
                };
              in
              derivedPkg;
          }
        );
      })
    ];
  };
}