kde5: add enableQt4Support option

nixos/modules/installer/cd-dvd/installation-cd-graphical-kde.nix

@@ -18,7 +18,10 @@ with lib;
       autoLogin = true;
     };
 
-    desktopManager.kde5.enable = true;
+    desktopManager.kde5 = {
+      enable = true;
+      enableQt4Support = false;
+    };
 
     # Enable touchpad support for many laptops.
     synaptics.enable = true;

nixos/modules/services/x11/desktop-managers/kde5.nix

@@ -22,6 +22,15 @@ in
         description = "Enable the Plasma 5 (KDE 5) desktop environment.";
       };
 
+      enableQt4Support = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Enable support for Qt 4-based applications. Particularly, install the
+          Qt 4 version of the Breeze theme and a default backend for Phonon.
+        '';
+      };
+
     };
 
   };
@@ -105,7 +114,7 @@ in
         kde5.sonnet
         kde5.threadweaver
 
-        kde5.breeze
+        kde5.breeze-qt5
         kde5.kactivitymanagerd
         kde5.kde-cli-tools
         kde5.kdecoration
@@ -160,6 +169,8 @@ in
       # frameworkintegration was split with plasma-integration in Plasma 5.6
       ++ lib.optional (lib.hasAttr "plasma-integration" kde5) kde5.plasma-integration
 
+      ++ lib.optionals cfg.enableQt4Support [ kde5.breeze-qt4 pkgs.phonon-backend-gstreamer ]
+
       # Optional hardware support features
       ++ lib.optional config.hardware.bluetooth.enable kde5.bluedevil
       ++ lib.optional config.networking.networkmanager.enable kde5.plasma-nm

pkgs/desktops/kde-5/plasma/default.nix

@@ -44,14 +44,6 @@ let
       inherit (srcs.breeze) src version;
     };
     breeze-qt5 = callPackage ./breeze-qt5.nix {};
-    breeze =
-      let
-        version = (builtins.parseDrvName breeze-qt5.name).version;
-      in
-        symlinkJoin {
-          name = "breeze-${version}";
-          paths = map (pkg: pkg.out or pkg) [ breeze-gtk breeze-qt4 breeze-qt5 ];
-        };
     breeze-grub = callPackage ./breeze-grub.nix {};
     breeze-plymouth = callPackage ./breeze-plymouth {};
     kactivitymanagerd = callPackage ./kactivitymanagerd.nix {};