kde: apply Qt theme on non-KDE systems and add Qt6 support

modules/kde/hm.nix

@@ -219,53 +219,80 @@ let
     printf '%s\n' "$kded5rc" >"$out/kded5rc"
     printf '%s\n' "$kdeglobals" >"$out/kdeglobals"
   '';
+
+  envVars = {
+    QT_QPA_PLATFORMTHEME = "kde"; 
+    QT_STYLE_OVERRIDE = "breeze";
+  }; 
 
 in {
   options.stylix.targets.kde.enable =
     config.lib.stylix.mkEnableTarget "KDE" true;
 
   config = lib.mkIf (config.stylix.enable && config.stylix.targets.kde.enable && pkgs.stdenv.hostPlatform.isLinux) {
-    home.packages = [ themePackage ];
-    xdg.systemDirs.config = [ "${configPackage}" ];
-
-    # plasma-apply-wallpaperimage is necessary to change the wallpaper
-    # after the first login.
-    #
-    # plasma-apply-lookandfeel is only here to trigger a hot reload, the theme
-    # would still be applied without it if you logged out and back in.
-    #
-    # Home Manager clears $PATH before running the activation script, but we
-    # want to avoid installing these tools explicitly because that would pull
-    # in large dependencies for people who aren't actually using KDE.
-    # The workaround used is to assume a list of common paths where the tools
-    # might be installed, and look there. The ideal solution would require
-    # changes to KDE to make it possible to update the wallpaper through
-    # config files alone.
-    home.activation.stylixLookAndFeel = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
-      global_path() {
-        for directory in /run/current-system/sw/bin /usr/bin /bin; do
-          if [[ -f "$directory/$1" ]]; then
-            printf '%s\n' "$directory/$1"
-            return 0
-          fi
-        done
-
-        return 1
-      }
-
-      if wallpaper_image="$(global_path plasma-apply-wallpaperimage)"; then
-        "$wallpaper_image" "${themePackage}/share/wallpapers/stylix"
-      else
-        verboseEcho \
-          "plasma-apply-wallpaperimage: command not found"
-      fi
-
-      if look_and_feel="$(global_path plasma-apply-lookandfeel)"; then
-        "$look_and_feel" --apply stylix
-      else
-        verboseEcho \
-          "Skipping plasma-apply-lookandfeel: command not found"
-      fi
-    '';
+    xdg = {
+      systemDirs.config = [ "${configPackage}" ];
+      configFile."kdeglobals".text = "${formatConfig colorscheme}";
+    };
+
+    systemd.user.sessionVariables = envVars;
+
+    qt = {
+      enable = true;
+    };
+
+    home = {
+      packages = with pkgs; [
+        themePackage
+
+        # QT6 packages (note that full does not mean "install all of KDE", just all of Qt6)
+        (hiPrio kdePackages.full)
+        (hiPrio kdePackages.breeze-icons)
+        (hiPrio kdePackages.breeze)
+        (hiPrio kdePackages.plasma-integration)
+        (hiPrio kdePackages.qqc2-breeze-style)
+        (hiPrio kdePackages.qqc2-desktop-style)
+
+        # QT5 packages
+        libsForQt5.full
+        libsForQt5.breeze-icons
+        libsForQt5.breeze-qt5
+        libsForQt5.qqc2-breeze-style
+        libsForQt5.qqc2-desktop-style
+        libsForQt5.plasma-integration
+      ];
+
+      sessionVariables = envVars;
+
+      # plasma-apply-wallpaperimage is necessary to change the wallpaper
+      # after the first login.
+      #
+      # Home Manager clears $PATH before running the activation script, but we
+      # want to avoid installing these tools explicitly because that would pull
+      # in large dependencies for people who aren't actually using KDE.
+      # The workaround used is to assume a list of common paths where the tools
+      # might be installed, and look there. The ideal solution would require
+      # changes to KDE to make it possible to update the wallpaper through
+      # config files alone.
+      activation.stylixLookAndFeel = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+        global_path() {
+          for directory in /run/current-system/sw/bin /usr/bin /bin; do
+            if [[ -f "$directory/$1" ]]; then
+              printf '%s\n' "$directory/$1"
+              return 0
+            fi
+          done
+
+          return 1
+        }
+
+        if wallpaper_image="$(global_path plasma-apply-wallpaperimage)"; then
+          "$wallpaper_image" "${themePackage}/share/wallpapers/stylix"
+        else
+          verboseEcho \
+            "plasma-apply-wallpaperimage: command not found"
+        fi
+      '';
+    };
   };
 }