Merge master into staging-next

44 files changed, 461 insertions, 357 deletions

diff --git a/nixos/doc/manual/configuration/x-windows.xml b/nixos/doc/manual/configuration/x-windows.xml
index 9206f43ea39..55ad9fe6e65 100644
--- a/nixos/doc/manual/configuration/x-windows.xml
+++ b/nixos/doc/manual/configuration/x-windows.xml
@@ -83,8 +83,7 @@
   desktop environment. If you wanted no desktop environment and i3 as your your
   window manager, you'd define:
 <programlisting>
-<xref linkend="opt-services.xserver.desktopManager.default"/> = "none";
-<xref linkend="opt-services.xserver.windowManager.default"/> = "i3";
+<xref linkend="opt-services.xserver.displayManager.defaultSession"/> = "none+i3";
 </programlisting>
   And, finally, to enable auto-login for a user <literal>johndoe</literal>:
 <programlisting>
diff --git a/nixos/doc/manual/configuration/xfce.xml b/nixos/doc/manual/configuration/xfce.xml
index 6ac99c6b2be..027828bb936 100644
--- a/nixos/doc/manual/configuration/xfce.xml
+++ b/nixos/doc/manual/configuration/xfce.xml
@@ -7,9 +7,8 @@
  <para>
   To enable the Xfce Desktop Environment, set
 <programlisting>
-<link linkend="opt-services.xserver.desktopManager.default">services.xserver.desktopManager</link> = {
-  <link linkend="opt-services.xserver.desktopManager.xfce.enable">xfce.enable</link> = true;
-  <link linkend="opt-services.xserver.desktopManager.default">default</link> = "xfce";
+<xref linkend="opt-services.xserver.desktopManager.xfce.enable" /> = true;
+<xref linkend="opt-services.xserver.displayManager.defaultSession" /> = "xfce";
 };
 </programlisting>
  </para>
diff --git a/nixos/doc/manual/man-nixos-option.xml b/nixos/doc/manual/man-nixos-option.xml
index beabf020c92..b82f3125609 100644
--- a/nixos/doc/manual/man-nixos-option.xml
+++ b/nixos/doc/manual/man-nixos-option.xml
@@ -119,4 +119,13 @@ Defined by:
    bug, please report to Nicolas Pierron.
   </para>
  </refsection>
+ <refsection>
+  <title>See also</title>
+  <para>
+   <citerefentry>
+    <refentrytitle>configuration.nix</refentrytitle>
+    <manvolnum>5</manvolnum>
+   </citerefentry>
+  </para>
+ </refsection>
 </refentry>
diff --git a/nixos/doc/manual/release-notes/rl-2003.xml b/nixos/doc/manual/release-notes/rl-2003.xml
index 2a38b2adbbb..247e9cd063c 100644
--- a/nixos/doc/manual/release-notes/rl-2003.xml
+++ b/nixos/doc/manual/release-notes/rl-2003.xml
@@ -55,6 +55,19 @@
       and adding a <option>--all</option> option which prints all options and their values.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     <option>services.xserver.desktopManager.default</option> and <option>services.xserver.windowManager.default</option> options were replaced by a single <xref linkend="opt-services.xserver.displayManager.defaultSession"/> option to improve support for upstream session files. If you used something like:
+<programlisting>
+services.xserver.desktopManager.default = "xfce";
+services.xserver.windowManager.default = "icewm";
+</programlisting>
+     you should change it to:
+<programlisting>
+services.xserver.displayManager.defaultSession = "xfce+icewm";
+</programlisting>
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 
diff --git a/nixos/lib/testing-python.nix b/nixos/lib/testing-python.nix
index d567d268765..c4eb9328b1d 100644
--- a/nixos/lib/testing-python.nix
+++ b/nixos/lib/testing-python.nix
@@ -262,9 +262,8 @@ in rec {
           virtualisation.memorySize = 1024;
           services.xserver.enable = true;
           services.xserver.displayManager.auto.enable = true;
-          services.xserver.windowManager.default = "icewm";
+          services.xserver.displayManager.defaultSession = "none+icewm";
           services.xserver.windowManager.icewm.enable = true;
-          services.xserver.desktopManager.default = "none";
         };
     in
       runInMachine ({
diff --git a/nixos/lib/testing.nix b/nixos/lib/testing.nix
index a5f060a8d8e..ae8ecd6270c 100644
--- a/nixos/lib/testing.nix
+++ b/nixos/lib/testing.nix
@@ -249,9 +249,8 @@ in rec {
           virtualisation.memorySize = 1024;
           services.xserver.enable = true;
           services.xserver.displayManager.auto.enable = true;
-          services.xserver.windowManager.default = "icewm";
+          services.xserver.displayManager.defaultSession = "none+icewm";
           services.xserver.windowManager.icewm.enable = true;
-          services.xserver.desktopManager.default = "none";
         };
     in
       runInMachine ({
diff --git a/nixos/modules/programs/sway.nix b/nixos/modules/programs/sway.nix
index 9a15c773463..d685a525932 100644
--- a/nixos/modules/programs/sway.nix
+++ b/nixos/modules/programs/sway.nix
@@ -24,6 +24,7 @@ let
   swayJoined = pkgs.symlinkJoin {
     name = "sway-joined";
     paths = [ swayWrapped swayPackage ];
+    passthru.providedSessions = [ "sway" ];
   };
 in {
   options.programs.sway = {
@@ -88,7 +89,7 @@ in {
     fonts.enableDefaultFonts = mkDefault true;
     programs.dconf.enable = mkDefault true;
     # To make a Sway session available if a display manager like SDDM is enabled:
-    services.xserver.displayManager.extraSessionFilePackages = [ swayJoined ];
+    services.xserver.displayManager.sessionPackages = [ swayJoined ];
   };
 
   meta.maintainers = with lib.maintainers; [ gnidorah primeos colemickens ];
diff --git a/nixos/modules/services/x11/desktop-managers/default.nix b/nixos/modules/services/x11/desktop-managers/default.nix
index 671a959cdde..534551c0c4a 100644
--- a/nixos/modules/services/x11/desktop-managers/default.nix
+++ b/nixos/modules/services/x11/desktop-managers/default.nix
@@ -86,23 +86,14 @@ in
       };
 
       default = mkOption {
-        type = types.str;
-        default = "";
+        type = types.nullOr types.str;
+        default = null;
         example = "none";
-        description = "Default desktop manager loaded if none have been chosen.";
-        apply = defaultDM:
-          if defaultDM == "" && cfg.session.list != [] then
-            (head cfg.session.list).name
-          else if any (w: w.name == defaultDM) cfg.session.list then
-            defaultDM
-          else
-            builtins.trace ''
-              Default desktop manager (${defaultDM}) not found at evaluation time.
-              These are the known valid session names:
-                ${concatMapStringsSep "\n  " (w: "services.xserver.desktopManager.default = \"${w.name}\";") cfg.session.list}
-              It's also possible the default can be found in one of these packages:
-                ${concatMapStringsSep "\n  " (p: p.name) config.services.xserver.displayManager.extraSessionFilePackages}
-            '' defaultDM;
+        description = ''
+          <emphasis role="strong">Deprecated</emphasis>, please use <xref linkend="opt-services.xserver.displayManager.defaultSession"/> instead.
+
+          Default desktop manager loaded if none have been chosen.
+        '';
       };
 
     };
diff --git a/nixos/modules/services/x11/desktop-managers/gnome3.nix b/nixos/modules/services/x11/desktop-managers/gnome3.nix
index 6725595e1cf..6d9bd284bc7 100644
--- a/nixos/modules/services/x11/desktop-managers/gnome3.nix
+++ b/nixos/modules/services/x11/desktop-managers/gnome3.nix
@@ -144,7 +144,7 @@ in
       services.gnome3.core-shell.enable = true;
       services.gnome3.core-utilities.enable = mkDefault true;
 
-      services.xserver.displayManager.extraSessionFilePackages = [ pkgs.gnome3.gnome-session ];
+      services.xserver.displayManager.sessionPackages = [ pkgs.gnome3.gnome-session ];
 
       environment.extraInit = ''
         ${concatMapStrings (p: ''
@@ -171,7 +171,7 @@ in
     })
 
     (mkIf flashbackEnabled {
-      services.xserver.displayManager.extraSessionFilePackages =  map
+      services.xserver.displayManager.sessionPackages =  map
         (wm: pkgs.gnome3.gnome-flashback.mkSessionForWm {
           inherit (wm) wmName wmLabel wmCommand;
         }) (optional cfg.flashback.enableMetacity {
diff --git a/nixos/modules/services/x11/desktop-managers/pantheon.nix b/nixos/modules/services/x11/desktop-managers/pantheon.nix
index 99db5b17b64..e07d5b5eaad 100644
--- a/nixos/modules/services/x11/desktop-managers/pantheon.nix
+++ b/nixos/modules/services/x11/desktop-managers/pantheon.nix
@@ -69,7 +69,7 @@ in
 
   config = mkIf cfg.enable {
 
-    services.xserver.displayManager.extraSessionFilePackages = [ pkgs.pantheon.elementary-session-settings ];
+    services.xserver.displayManager.sessionPackages = [ pkgs.pantheon.elementary-session-settings ];
 
     # Ensure lightdm is used when Pantheon is enabled
     # Without it screen locking will be nonfunctional because of the use of lightlocker
@@ -81,9 +81,9 @@ in
 
     services.xserver.displayManager.lightdm.greeters.pantheon.enable = mkDefault true;
 
-    # If not set manually Pantheon session cannot be started
-    # Known issue of https://github.com/NixOS/nixpkgs/pull/43992
-    services.xserver.desktopManager.default = mkForce "pantheon";
+    # Without this, Elementary LightDM greeter will pre-select non-existent `default` session
+    # https://github.com/elementary/greeter/issues/368
+    services.xserver.displayManager.defaultSession = "pantheon";
 
     services.xserver.displayManager.sessionCommands = ''
       if test "$XDG_CURRENT_DESKTOP" = "Pantheon"; then
diff --git a/nixos/modules/services/x11/desktop-managers/surf-display.nix b/nixos/modules/services/x11/desktop-managers/surf-display.nix
index 140dde828da..9aeb0bbd2a8 100644
--- a/nixos/modules/services/x11/desktop-managers/surf-display.nix
+++ b/nixos/modules/services/x11/desktop-managers/surf-display.nix
@@ -118,7 +118,7 @@ in {
   };
 
   config = mkIf cfg.enable {
-    services.xserver.displayManager.extraSessionFilePackages = [
+    services.xserver.displayManager.sessionPackages = [
       pkgs.surf-display
     ];
 
diff --git a/nixos/modules/services/x11/display-managers/account-service-util.nix b/nixos/modules/services/x11/display-managers/account-service-util.nix
new file mode 100644
index 00000000000..1dbe703b566
--- /dev/null
+++ b/nixos/modules/services/x11/display-managers/account-service-util.nix
@@ -0,0 +1,39 @@
+{ accountsservice
+, glib
+, gobject-introspection
+, python3
+, wrapGAppsHook
+}:
+
+python3.pkgs.buildPythonApplication {
+  name = "set-session";
+
+  format = "other";
+
+  src = ./set-session.py;
+
+  dontUnpack = true;
+
+  strictDeps = false;
+
+  nativeBuildInputs = [
+    wrapGAppsHook
+    gobject-introspection
+  ];
+
+  buildInputs = [
+    accountsservice
+    glib
+  ];
+
+  propagatedBuildInputs = with python3.pkgs; [
+    pygobject3
+    ordered-set
+  ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    cp $src $out/bin/set-session
+    chmod +x $out/bin/set-session
+  '';
+}
diff --git a/nixos/modules/services/x11/display-managers/default.nix b/nixos/modules/services/x11/display-managers/default.nix
index c252c3c90c9..2d809b5cc9f 100644
--- a/nixos/modules/services/x11/display-managers/default.nix
+++ b/nixos/modules/services/x11/display-managers/default.nix
@@ -27,16 +27,7 @@ let
     Xft.hintstyle: hintslight
   '';
 
-  mkCases = session:
-    concatStrings (
-      mapAttrsToList (name: starts: ''
-                       (${name})
-                         ${concatMapStringsSep "\n  " (n: n.start) starts}
-                         ;;
-                     '') (lib.groupBy (n: n.name) session)
-    );
-
-  # file provided by services.xserver.displayManager.session.wrapper
+  # file provided by services.xserver.displayManager.sessionData.wrapper
   xsessionWrapper = pkgs.writeScript "xsession-wrapper"
     ''
       #! ${pkgs.bash}/bin/bash
@@ -116,94 +107,44 @@ let
           # Run the supplied session command. Remove any double quotes with eval.
           eval exec "$@"
       else
-          # Fall back to the default window/desktopManager
-          exec ${cfg.displayManager.session.script}
+          # TODO: Do we need this? Should not the session always exist?
+          echo "error: unknown session $1" 1>&2
+          exit 1
       fi
     '';
 
-  # file provided by services.xserver.displayManager.session.script
-  xsession = wm: dm: pkgs.writeScript "xsession"
-    ''
-      #! ${pkgs.bash}/bin/bash
-
-      # Legacy session script used to construct .desktop files from
-      # `services.xserver.displayManager.session` entries. Called from
-      # `sessionWrapper`.
-
-      # Expected parameters:
-      #   $1 = <desktop-manager>+<window-manager>
-
-      # The first argument of this script is the session type.
-      sessionType="$1"
-      if [ "$sessionType" = default ]; then sessionType=""; fi
-
-      # The session type is "<desktop-manager>+<window-manager>", so
-      # extract those (see:
-      # http://wiki.bash-hackers.org/syntax/pe#substring_removal).
-      windowManager="''${sessionType##*+}"
-      : ''${windowManager:=${cfg.windowManager.default}}
-      desktopManager="''${sessionType%%+*}"
-      : ''${desktopManager:=${cfg.desktopManager.default}}
-
-      # Start the window manager.
-      case "$windowManager" in
-        ${mkCases wm}
-        (*) echo "$0: Window manager '$windowManager' not found.";;
-      esac
-
-      # Start the desktop manager.
-      case "$desktopManager" in
-        ${mkCases dm}
-        (*) echo "$0: Desktop manager '$desktopManager' not found.";;
-      esac
-
-      ${optionalString cfg.updateDbusEnvironment ''
-        ${lib.getBin pkgs.dbus}/bin/dbus-update-activation-environment --systemd --all
-      ''}
-
-      test -n "$waitPID" && wait "$waitPID"
-
-      ${config.systemd.package}/bin/systemctl --user stop graphical-session.target
-
-      exit 0
-    '';
-
-  # Desktop Entry Specification:
-  # - https://standards.freedesktop.org/desktop-entry-spec/latest/
-  # - https://standards.freedesktop.org/desktop-entry-spec/latest/ar01s06.html
-  mkDesktops = names: pkgs.runCommand "desktops"
+  installedSessions = pkgs.runCommand "desktops"
     { # trivial derivation
       preferLocalBuild = true;
       allowSubstitutes = false;
     }
     ''
-      mkdir -p "$out/share/xsessions"
-      ${concatMapStrings (n: ''
-        cat - > "$out/share/xsessions/${n}.desktop" << EODESKTOP
-        [Desktop Entry]
-        Version=1.0
-        Type=XSession
-        TryExec=${cfg.displayManager.session.script}
-        Exec=${cfg.displayManager.session.script} "${n}"
-        Name=${n}
-        Comment=
-        EODESKTOP
-      '') names}
+      mkdir -p "$out/share/"{xsessions,wayland-sessions}
 
       ${concatMapStrings (pkg: ''
+        for n in ${concatStringsSep " " pkg.providedSessions}; do
+          if ! test -f ${pkg}/share/wayland-sessions/$n.desktop -o \
+                    -f ${pkg}/share/xsessions/$n.desktop; then
+            echo "Couldn't find provided session name, $n.desktop, in session package ${pkg.name}:"
+            echo "  ${pkg}"
+            return 1
+          fi
+        done
+
         if test -d ${pkg}/share/xsessions; then
           ${xorg.lndir}/bin/lndir ${pkg}/share/xsessions $out/share/xsessions
         fi
-      '') cfg.displayManager.extraSessionFilePackages}
-
-      ${concatMapStrings (pkg: ''
         if test -d ${pkg}/share/wayland-sessions; then
-          mkdir -p "$out/share/wayland-sessions"
           ${xorg.lndir}/bin/lndir ${pkg}/share/wayland-sessions $out/share/wayland-sessions
         fi
-      '') cfg.displayManager.extraSessionFilePackages}
+      '') cfg.displayManager.sessionPackages}
     '';
 
+  dmDefault = cfg.desktopManager.default;
+  wmDefault = cfg.windowManager.default;
+
+  defaultSessionFromLegacyOptions = concatStringsSep "+" (filter (s: s != null) ([ dmDefault ] ++ optional (wmDefault != "none") wmDefault));
+
 in
 
 {
@@ -261,11 +202,24 @@ in
         '';
       };
 
-      extraSessionFilePackages = mkOption {
-        type = types.listOf types.package;
+      sessionPackages = mkOption {
+        type = with types; listOf (package // {
+          description = "package with provided sessions";
+          check = p: assertMsg
+            (package.check p && p ? providedSessions
+            && p.providedSessions != [] && all isString p.providedSessions)
+            ''
+              Package, '${p.name}', did not specify any session names, as strings, in
+              'passthru.providedSessions'. This is required when used as a session package.
+
+              The session names can be looked up in:
+                ${p}/share/xsessions
+                ${p}/share/wayland-sessions
+           '';
+        });
         default = [];
         description = ''
-          A list of packages containing xsession files to be passed to the display manager.
+          A list of packages containing x11 or wayland session files to be passed to the display manager.
         '';
       };
 
@@ -296,18 +250,50 @@ in
           inside the display manager with the desktop manager name
           followed by the window manager name.
         '';
-        apply = list: rec {
-          wm = filter (s: s.manage == "window") list;
-          dm = filter (s: s.manage == "desktop") list;
-          names = flip concatMap dm
-            (d: map (w: d.name + optionalString (w.name != "none") ("+" + w.name))
-              (filter (w: d.name != "none" || w.name != "none") wm));
-          desktops = mkDesktops names;
-          script = xsession wm dm;
+      };
+
+      sessionData = mkOption {
+        description = "Data exported for display managers’ convenience";
+        internal = true;
+        default = {};
+        apply = val: {
           wrapper = xsessionWrapper;
+          desktops = installedSessions;
+          sessionNames = concatMap (p: p.providedSessions) cfg.displayManager.sessionPackages;
+          # We do not want to force users to set defaultSession when they have only single DE.
+          autologinSession =
+            if cfg.displayManager.defaultSession != null then
+              cfg.displayManager.defaultSession
+            else if cfg.displayManager.sessionData.sessionNames != [] then
+              head cfg.displayManager.sessionData.sessionNames
+            else
+              null;
         };
       };
 
+      defaultSession = mkOption {
+        type = with types; nullOr str // {
+          description = "session name";
+          check = d:
+            assertMsg (d != null -> (str.check d && elem d cfg.displayManager.sessionData.sessionNames)) ''
+                Default graphical session, '${d}', not found.
+                Valid names for 'services.xserver.displayManager.defaultSession' are:
+                  ${concatStringsSep "\n  " cfg.displayManager.sessionData.sessionNames}
+              '';
+        };
+        default =
+          if dmDefault != null || wmDefault != null then
+            defaultSessionFromLegacyOptions
+          else
+            null;
+        example = "gnome";
+        description = ''
+          Graphical session to pre-select in the session chooser (only effective for GDM and LightDM).
+
+          On GDM, LightDM and SDDM, it will also be used as a session for auto-login.
+        '';
+      };
+
       job = {
 
         preStart = mkOption {
@@ -356,6 +342,27 @@ in
   };
 
   config = {
+    assertions = [
+      {
+        assertion = cfg.desktopManager.default != null || cfg.windowManager.default != null -> cfg.displayManager.defaultSession == defaultSessionFromLegacyOptions;
+        message = "You cannot use both services.xserver.displayManager.defaultSession option and legacy options (services.xserver.desktopManager.default and services.xserver.windowManager.default).";
+      }
+    ];
+
+    warnings =
+      mkIf (dmDefault != null || wmDefault != null) [
+        ''
+          The following options are deprecated:
+            ${concatStringsSep "\n  " (map ({c, t}: t) (filter ({c, t}: c != null) [
+            { c = dmDefault; t = "- services.xserver.desktopManager.default"; }
+            { c = wmDefault; t = "- services.xserver.windowManager.default"; }
+            ]))}
+          Please use
+            services.xserver.displayManager.defaultSession = "${concatStringsSep "+" (filter (s: s != null) [ dmDefault wmDefault ])}";
+          instead.
+        ''
+      ];
+
     services.xserver.displayManager.xserverBin = "${xorg.xorgserver.out}/bin/X";
 
     systemd.user.targets.graphical-session = {
@@ -364,6 +371,67 @@ in
         StopWhenUnneeded = false;
       };
     };
+
+    # Create desktop files and scripts for starting sessions for WMs/DMs
+    # that do not have upstream session files (those defined using services.{display,desktop,window}Manager.session options).
+    services.xserver.displayManager.sessionPackages =
+      let
+        dms = filter (s: s.manage == "desktop") cfg.displayManager.session;
+        wms = filter (s: s.manage == "window") cfg.displayManager.session;
+
+        # Script responsible for starting the window manager and the desktop manager.
+        xsession = wm: dm: pkgs.writeScript "xsession" ''
+          #! ${pkgs.bash}/bin/bash
+
+          # Legacy session script used to construct .desktop files from
+          # `services.xserver.displayManager.session` entries. Called from
+          # `sessionWrapper`.
+
+          # Start the window manager.
+          ${wm.start}
+
+          # Start the desktop manager.
+          ${dm.start}
+
+          ${optionalString cfg.updateDbusEnvironment ''
+            ${lib.getBin pkgs.dbus}/bin/dbus-update-activation-environment --systemd --all
+          ''}
+
+          test -n "$waitPID" && wait "$waitPID"
+
+          ${config.systemd.package}/bin/systemctl --user stop graphical-session.target
+
+          exit 0
+        '';
+      in
+        # We will generate every possible pair of WM and DM.
+        concatLists (
+          crossLists
+            (dm: wm: let
+              sessionName = "${dm.name}${optionalString (wm.name != "none") ("+" + wm.name)}";
+              script = xsession dm wm;
+            in
+              optional (dm.name != "none" || wm.name != "none")
+                (pkgs.writeTextFile {
+                  name = "${sessionName}-xsession";
+                  destination = "/share/xsessions/${sessionName}.desktop";
+                  # Desktop Entry Specification:
+                  # - https://standards.freedesktop.org/desktop-entry-spec/latest/
+                  # - https://standards.freedesktop.org/desktop-entry-spec/latest/ar01s06.html
+                  text = ''
+                    [Desktop Entry]
+                    Version=1.0
+                    Type=XSession
+                    TryExec=${script}
+                    Exec=${script}
+                    Name=${sessionName}
+                  '';
+                } // {
+                  providedSessions = [ sessionName ];
+                })
+            )
+            [dms wms]
+          );
   };
 
   imports = [
@@ -371,6 +439,7 @@ in
      "The option is no longer necessary because all display managers have already delegated lid management to systemd.")
     (mkRenamedOptionModule [ "services" "xserver" "displayManager" "job" "logsXsession" ] [ "services" "xserver" "displayManager" "job" "logToFile" ])
     (mkRenamedOptionModule [ "services" "xserver" "displayManager" "logToJournal" ] [ "services" "xserver" "displayManager" "job" "logToJournal" ])
+    (mkRenamedOptionModule [ "services" "xserver" "displayManager" "extraSessionFilesPackages" ] [ "services" "xserver" "displayManager" "sessionPackages" ])
   ];
 
 }
diff --git a/nixos/modules/services/x11/display-managers/gdm.nix b/nixos/modules/services/x11/display-managers/gdm.nix
index 095569fa08a..6630f012f04 100644
--- a/nixos/modules/services/x11/display-managers/gdm.nix
+++ b/nixos/modules/services/x11/display-managers/gdm.nix
@@ -31,44 +31,9 @@ let
     load-module module-position-event-sounds
   '';
 
-  dmDefault = config.services.xserver.desktopManager.default;
-  wmDefault = config.services.xserver.windowManager.default;
-  hasDefaultUserSession = dmDefault != "none" || wmDefault != "none";
-  defaultSessionName = dmDefault + optionalString (wmDefault != "none") ("+" + wmDefault);
-
-  setSessionScript = pkgs.python3.pkgs.buildPythonApplication {
-    name = "set-session";
-
-    format = "other";
-
-    src = ./set-session.py;
-
-    dontUnpack = true;
-
-    strictDeps = false;
-
-    nativeBuildInputs = with pkgs; [
-      wrapGAppsHook
-      gobject-introspection
-    ];
-
-    buildInputs = with pkgs; [
-      accountsservice
-      glib
-    ];
-
-    propagatedBuildInputs = with pkgs.python3.pkgs; [
-      pygobject3
-      ordered-set
-    ];
-
-    installPhase = ''
-      mkdir -p $out/bin
-      cp $src $out/bin/set-session
-      chmod +x $out/bin/set-session
-    '';
-  };
+  defaultSessionName = config.services.xserver.displayManager.defaultSession;
 
+  setSessionScript = pkgs.callPackage ./account-service-util.nix { };
 in
 
 {
@@ -186,7 +151,7 @@ in
         environment = {
           GDM_X_SERVER_EXTRA_ARGS = toString
             (filter (arg: arg != "-terminate") cfg.xserverArgs);
-          XDG_DATA_DIRS = "${cfg.session.desktops}/share/";
+          XDG_DATA_DIRS = "${cfg.sessionData.desktops}/share/";
         } // optionalAttrs (xSessionWrapper != null) {
           # Make GDM use this wrapper before running the session, which runs the
           # configured setupCommands. This relies on a patched GDM which supports
@@ -204,16 +169,19 @@ in
           cat - > /run/gdm/.config/gnome-initial-setup-done <<- EOF
           yes
           EOF
-        ''
-        # TODO: Make setSessionScript aware of previously used sessions
-        # + optionalString hasDefaultUserSession ''
-        #   ${setSessionScript}/bin/set-session ${defaultSessionName}
-        # ''
-        ;
+        '' + optionalString (defaultSessionName != null) ''
+          # Set default session in session chooser to a specified values – basically ignore session history.
+          ${setSessionScript}/bin/set-session ${cfg.sessionData.autologinSession}
+        '';
       };
 
-    # Because sd_login_monitor_new requires /run/systemd/machines
-    systemd.services.display-manager.wants = [ "systemd-machined.service" ];
+    systemd.services.display-manager.wants = [
+      # Because sd_login_monitor_new requires /run/systemd/machines
+      "systemd-machined.service"
+      # setSessionScript wants AccountsService
+      "accounts-daemon.service"
+    ];
+
     systemd.services.display-manager.after = [
       "rc-local.service"
       "systemd-machined.service"
@@ -329,7 +297,7 @@ in
       ${optionalString cfg.gdm.debug "Enable=true"}
     '';
 
-    environment.etc."gdm/Xsession".source = config.services.xserver.displayManager.session.wrapper;
+    environment.etc."gdm/Xsession".source = config.services.xserver.displayManager.sessionData.wrapper;
 
     # GDM LFS PAM modules, adapted somehow to NixOS
     security.pam.services = {
diff --git a/nixos/modules/services/x11/display-managers/lightdm-greeters/mini.nix b/nixos/modules/services/x11/display-managers/lightdm-greeters/mini.nix
index fa9445af32e..0025f9b3603 100644
--- a/nixos/modules/services/x11/display-managers/lightdm-greeters/mini.nix
+++ b/nixos/modules/services/x11/display-managers/lightdm-greeters/mini.nix
@@ -53,9 +53,8 @@ in
           Whether to enable lightdm-mini-greeter as the lightdm greeter.
 
           Note that this greeter starts only the default X session.
-          You can configure the default X session by
-          <option>services.xserver.desktopManager.default</option> and
-          <option>services.xserver.windowManager.default</option>.
+          You can configure the default X session using
+          <xref linkend="opt-services.xserver.displayManager.defaultSession"/>.
         '';
       };
 
diff --git a/nixos/modules/services/x11/display-managers/lightdm.nix b/nixos/modules/services/x11/display-managers/lightdm.nix
index cf4c05acbcc..f7face0adb7 100644
--- a/nixos/modules/services/x11/display-managers/lightdm.nix
+++ b/nixos/modules/services/x11/display-managers/lightdm.nix
@@ -8,10 +8,9 @@ let
   dmcfg = xcfg.displayManager;
   xEnv = config.systemd.services.display-manager.environment;
   cfg = dmcfg.lightdm;
+  sessionData = dmcfg.sessionData;
 
-  dmDefault = xcfg.desktopManager.default;
-  wmDefault = xcfg.windowManager.default;
-  hasDefaultUserSession = dmDefault != "none" || wmDefault != "none";
+  setSessionScript = pkgs.callPackage ./account-service-util.nix { };
 
   inherit (pkgs) lightdm writeScript writeText;
 
@@ -45,22 +44,19 @@ let
         greeter-user = ${config.users.users.lightdm.name}
         greeters-directory = ${cfg.greeter.package}
       ''}
-      sessions-directory = ${dmcfg.session.desktops}/share/xsessions
+      sessions-directory = ${dmcfg.sessionData.desktops}/share/xsessions:${dmcfg.sessionData.desktops}/share/wayland-sessions
       ${cfg.extraConfig}
 
       [Seat:*]
       xserver-command = ${xserverWrapper}
-      session-wrapper = ${dmcfg.session.wrapper}
+      session-wrapper = ${dmcfg.sessionData.wrapper}
       ${optionalString cfg.greeter.enable ''
         greeter-session = ${cfg.greeter.name}
       ''}
       ${optionalString cfg.autoLogin.enable ''
         autologin-user = ${cfg.autoLogin.user}
         autologin-user-timeout = ${toString cfg.autoLogin.timeout}
-        autologin-session = ${defaultSessionName}
-      ''}
-      ${optionalString hasDefaultUserSession ''
-        user-session=${defaultSessionName}
+        autologin-session = ${sessionData.autologinSession}
       ''}
       ${optionalString (dmcfg.setupCommands != "") ''
         display-setup-script=${pkgs.writeScript "lightdm-display-setup" ''
@@ -71,7 +67,6 @@ let
       ${cfg.extraSeatDefaults}
     '';
 
-  defaultSessionName = dmDefault + optionalString (wmDefault != "none") ("+" + wmDefault);
 in
 {
   # Note: the order in which lightdm greeter modules are imported
@@ -199,11 +194,9 @@ in
           LightDM auto-login requires services.xserver.displayManager.lightdm.autoLogin.user to be set
         '';
       }
-      { assertion = cfg.autoLogin.enable -> dmDefault != "none" || wmDefault != "none";
+      { assertion = cfg.autoLogin.enable -> sessionData.autologinSession != null;
         message = ''
-          LightDM auto-login requires that services.xserver.desktopManager.default and
-          services.xserver.windowManager.default are set to valid values. The current
-          default session: ${defaultSessionName} is not valid.
+          LightDM auto-login requires that services.xserver.displayManager.defaultSession is set.
         '';
       }
       { assertion = !cfg.greeter.enable -> (cfg.autoLogin.enable && cfg.autoLogin.timeout == 0);
@@ -214,6 +207,20 @@ in
       }
     ];
 
+    # Set default session in session chooser to a specified values – basically ignore session history.
+    # Auto-login is already covered by a config value.
+    services.xserver.displayManager.job.preStart = optionalString (!cfg.autoLogin.enable && dmcfg.defaultSession != null) ''
+      ${setSessionScript}/bin/set-session ${dmcfg.defaultSession}
+    '';
+
+    # setSessionScript needs session-files in XDG_DATA_DIRS
+    services.xserver.displayManager.job.environment.XDG_DATA_DIRS = "${dmcfg.sessionData.desktops}/share/";
+
+    # setSessionScript wants AccountsService
+    systemd.services.display-manager.wants = [
+      "accounts-daemon.service"
+    ];
+
     # lightdm relaunches itself via just `lightdm`, so needs to be on the PATH
     services.xserver.displayManager.job.execCmd = ''
       export PATH=${lightdm}/sbin:$PATH
diff --git a/nixos/modules/services/x11/display-managers/sddm.nix b/nixos/modules/services/x11/display-managers/sddm.nix
index 24e120c4f2c..4224c557ed6 100644
--- a/nixos/modules/services/x11/display-managers/sddm.nix
+++ b/nixos/modules/services/x11/display-managers/sddm.nix
@@ -50,8 +50,8 @@ let
     MinimumVT=${toString (if xcfg.tty != null then xcfg.tty else 7)}
     ServerPath=${xserverWrapper}
     XephyrPath=${pkgs.xorg.xorgserver.out}/bin/Xephyr
-    SessionCommand=${dmcfg.session.wrapper}
-    SessionDir=${dmcfg.session.desktops}/share/xsessions
+    SessionCommand=${dmcfg.sessionData.wrapper}
+    SessionDir=${dmcfg.sessionData.desktops}/share/xsessions
     XauthPath=${pkgs.xorg.xauth}/bin/xauth
     DisplayCommand=${Xsetup}
     DisplayStopCommand=${Xstop}
@@ -59,23 +59,19 @@ let
 
     [Wayland]
     EnableHidpi=${if cfg.enableHidpi then "true" else "false"}
-    SessionDir=${dmcfg.session.desktops}/share/wayland-sessions
+    SessionDir=${dmcfg.sessionData.desktops}/share/wayland-sessions
 
     ${optionalString cfg.autoLogin.enable ''
     [Autologin]
     User=${cfg.autoLogin.user}
-    Session=${defaultSessionName}.desktop
+    Session=${autoLoginSessionName}.desktop
     Relogin=${boolToString cfg.autoLogin.relogin}
     ''}
 
     ${cfg.extraConfig}
   '';
 
-  defaultSessionName =
-    let
-      dm = xcfg.desktopManager.default;
-      wm = xcfg.windowManager.default;
-    in dm + optionalString (wm != "none") ("+" + wm);
+  autoLoginSessionName = dmcfg.sessionData.autologinSession;
 
 in
 {
@@ -210,11 +206,9 @@ in
           SDDM auto-login requires services.xserver.displayManager.sddm.autoLogin.user to be set
         '';
       }
-      { assertion = cfg.autoLogin.enable -> elem defaultSessionName dmcfg.session.names;
+      { assertion = cfg.autoLogin.enable -> autoLoginSessionName != null;
         message = ''
-          SDDM auto-login requires that services.xserver.desktopManager.default and
-          services.xserver.windowManager.default are set to valid values. The current
-          default session: ${defaultSessionName} is not valid.
+          SDDM auto-login requires that services.xserver.displayManager.defaultSession is set.
         '';
       }
     ];
diff --git a/nixos/modules/services/x11/window-managers/default.nix b/nixos/modules/services/x11/window-managers/default.nix
index c17f3830d0e..04a9fc46628 100644
--- a/nixos/modules/services/x11/window-managers/default.nix
+++ b/nixos/modules/services/x11/window-managers/default.nix
@@ -59,15 +59,14 @@ in
       };
 
       default = mkOption {
-        type = types.str;
-        default = "none";
+        type = types.nullOr types.str;
+        default = null;
         example = "wmii";
-        description = "Default window manager loaded if none have been chosen.";
-        apply = defaultWM:
-          if any (w: w.name == defaultWM) cfg.session then
-            defaultWM
-          else
-            throw "Default window manager (${defaultWM}) not found.";
+        description = ''
+          <emphasis role="strong">Deprecated</emphasis>, please use <xref linkend="opt-services.xserver.displayManager.defaultSession"/> instead.
+
+          Default window manager loaded if none have been chosen.
+        '';
       };
 
     };
diff --git a/nixos/tests/common/x11.nix b/nixos/tests/common/x11.nix
index c5a7c165d12..5ad0ac20fac 100644
--- a/nixos/tests/common/x11.nix
+++ b/nixos/tests/common/x11.nix
@@ -1,12 +1,12 @@
+{ lib, ... }:
+
 { services.xserver.enable = true;
 
   # Automatically log in.
   services.xserver.displayManager.auto.enable = true;
 
   # Use IceWM as the window manager.
-  services.xserver.windowManager.default = "icewm";
-  services.xserver.windowManager.icewm.enable = true;
-
   # Don't use a desktop manager.
-  services.xserver.desktopManager.default = "none";
+  services.xserver.displayManager.defaultSession = lib.mkDefault "none+icewm";
+  services.xserver.windowManager.icewm.enable = true;
 }
diff --git a/nixos/tests/gnome3-xorg.nix b/nixos/tests/gnome3-xorg.nix
index eb4c376319b..aa03501f6a5 100644
--- a/nixos/tests/gnome3-xorg.nix
+++ b/nixos/tests/gnome3-xorg.nix
@@ -16,7 +16,7 @@ import ./make-test.nix ({ pkgs, ...} : {
       services.xserver.displayManager.lightdm.autoLogin.enable = true;
       services.xserver.displayManager.lightdm.autoLogin.user = "alice";
       services.xserver.desktopManager.gnome3.enable = true;
-      services.xserver.desktopManager.default = "gnome-xorg";
+      services.xserver.displayManager.defaultSession = "gnome-xorg";
 
       virtualisation.memorySize = 1024;
     };
diff --git a/nixos/tests/hadoop/hdfs.nix b/nixos/tests/hadoop/hdfs.nix
index e7d72a56e1e..85aaab34b15 100644
--- a/nixos/tests/hadoop/hdfs.nix
+++ b/nixos/tests/hadoop/hdfs.nix
@@ -1,4 +1,4 @@
-import ../make-test.nix ({...}: {
+import ../make-test-python.nix ({...}: {
   nodes = {
     namenode = {pkgs, ...}: {
       services.hadoop = {
@@ -35,20 +35,20 @@ import ../make-test.nix ({...}: {
   };
 
   testScript = ''
-    startAll
+    start_all()
 
-    $namenode->waitForUnit("hdfs-namenode");
-    $namenode->waitForUnit("network.target");
-    $namenode->waitForOpenPort(8020);
-    $namenode->waitForOpenPort(9870);
+    namenode.wait_for_unit("hdfs-namenode")
+    namenode.wait_for_unit("network.target")
+    namenode.wait_for_open_port(8020)
+    namenode.wait_for_open_port(9870)
 
-    $datanode->waitForUnit("hdfs-datanode");
-    $datanode->waitForUnit("network.target");
-    $datanode->waitForOpenPort(9864);
-    $datanode->waitForOpenPort(9866);
-    $datanode->waitForOpenPort(9867);
+    datanode.wait_for_unit("hdfs-datanode")
+    datanode.wait_for_unit("network.target")
+    datanode.wait_for_open_port(9864)
+    datanode.wait_for_open_port(9866)
+    datanode.wait_for_open_port(9867)
 
-    $namenode->succeed("curl http://namenode:9870");
-    $datanode->succeed("curl http://datanode:9864");
+    namenode.succeed("curl http://namenode:9870")
+    datanode.succeed("curl http://datanode:9864")
   '';
 })
diff --git a/nixos/tests/hadoop/yarn.nix b/nixos/tests/hadoop/yarn.nix
index 031592301f1..2264ecaff15 100644
--- a/nixos/tests/hadoop/yarn.nix
+++ b/nixos/tests/hadoop/yarn.nix
@@ -1,4 +1,4 @@
-import ../make-test.nix ({...}: {
+import ../make-test-python.nix ({...}: {
   nodes = {
     resourcemanager = {pkgs, ...}: {
       services.hadoop.package = pkgs.hadoop_3_1;
@@ -28,19 +28,19 @@ import ../make-test.nix ({...}: {
   };
 
   testScript = ''
-    startAll;
+    start_all()
 
-    $resourcemanager->waitForUnit("yarn-resourcemanager");
-    $resourcemanager->waitForUnit("network.target");
-    $resourcemanager->waitForOpenPort(8031);
-    $resourcemanager->waitForOpenPort(8088);
+    resourcemanager.wait_for_unit("yarn-resourcemanager")
+    resourcemanager.wait_for_unit("network.target")
+    resourcemanager.wait_for_open_port(8031)
+    resourcemanager.wait_for_open_port(8088)
 
-    $nodemanager->waitForUnit("yarn-nodemanager");
-    $nodemanager->waitForUnit("network.target");
-    $nodemanager->waitForOpenPort(8042);
-    $nodemanager->waitForOpenPort(8041);
+    nodemanager.wait_for_unit("yarn-nodemanager")
+    nodemanager.wait_for_unit("network.target")
+    nodemanager.wait_for_open_port(8042)
+    nodemanager.wait_for_open_port(8041)
 
-    $resourcemanager->succeed("curl http://localhost:8088");
-    $nodemanager->succeed("curl http://localhost:8042");
+    resourcemanager.succeed("curl http://localhost:8088")
+    nodemanager.succeed("curl http://localhost:8042")
   '';
 })
diff --git a/nixos/tests/haproxy.nix b/nixos/tests/haproxy.nix
index 72e77a68193..b6fed3e2108 100644
--- a/nixos/tests/haproxy.nix
+++ b/nixos/tests/haproxy.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs, ...}: {
+import ./make-test-python.nix ({ pkgs, ...}: {
   name = "haproxy";
   nodes = {
     machine = { ... }: {
@@ -33,11 +33,13 @@ import ./make-test.nix ({ pkgs, ...}: {
     };
   };
   testScript = ''
-    startAll;
-    $machine->waitForUnit('multi-user.target');
-    $machine->waitForUnit('haproxy.service');
-    $machine->waitForUnit('httpd.service');
-    $machine->succeed('curl -k http://localhost:80/index.txt | grep "We are all good!"');
-    $machine->succeed('curl -k http://localhost:80/metrics | grep haproxy_process_pool_allocated_bytes');
+    start_all()
+    machine.wait_for_unit("multi-user.target")
+    machine.wait_for_unit("haproxy.service")
+    machine.wait_for_unit("httpd.service")
+    assert "We are all good!" in machine.succeed("curl -k http://localhost:80/index.txt")
+    assert "haproxy_process_pool_allocated_bytes" in machine.succeed(
+        "curl -k http://localhost:80/metrics"
+    )
   '';
 })
diff --git a/nixos/tests/hitch/default.nix b/nixos/tests/hitch/default.nix
index cb24c4dcffc..10612025641 100644
--- a/nixos/tests/hitch/default.nix
+++ b/nixos/tests/hitch/default.nix
@@ -1,4 +1,4 @@
-import ../make-test.nix ({ pkgs, ... }:
+import ../make-test-python.nix ({ pkgs, ... }:
 {
   name = "hitch";
   meta = with pkgs.stdenv.lib.maintainers; {
@@ -23,11 +23,11 @@ import ../make-test.nix ({ pkgs, ... }:
 
   testScript =
     ''
-      startAll;
+      start_all()
 
-      $machine->waitForUnit('multi-user.target');
-      $machine->waitForUnit('hitch.service');
-      $machine->waitForOpenPort(443);
-      $machine->succeed('curl -k https://localhost:443/index.txt | grep "We are all good!"');
+      machine.wait_for_unit("multi-user.target")
+      machine.wait_for_unit("hitch.service")
+      machine.wait_for_open_port(443)
+      assert "We are all good!" in machine.succeed("curl -k https://localhost:443/index.txt")
     '';
 })
diff --git a/nixos/tests/i3wm.nix b/nixos/tests/i3wm.nix
index 8afa845f1e2..126178d1187 100644
--- a/nixos/tests/i3wm.nix
+++ b/nixos/tests/i3wm.nix
@@ -7,7 +7,7 @@ import ./make-test-python.nix ({ pkgs, ...} : {
   machine = { lib, ... }: {
     imports = [ ./common/x11.nix ./common/user-account.nix ];
     services.xserver.displayManager.auto.user = "alice";
-    services.xserver.windowManager.default = lib.mkForce "i3";
+    services.xserver.displayManager.defaultSession = lib.mkForce "none+i3";
     services.xserver.windowManager.i3.enable = true;
   };
 
diff --git a/nixos/tests/initrd-network.nix b/nixos/tests/initrd-network.nix
index ed9b82e2da7..4796ff9b7c8 100644
--- a/nixos/tests/initrd-network.nix
+++ b/nixos/tests/initrd-network.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs, ...} : {
+import ./make-test-python.nix ({ pkgs, ...} : {
   name = "initrd-network";
 
   meta.maintainers = [ pkgs.stdenv.lib.maintainers.eelco ];
@@ -15,8 +15,8 @@ import ./make-test.nix ({ pkgs, ...} : {
 
   testScript =
     ''
-      startAll;
-      $machine->waitForUnit("multi-user.target");
-      $machine->succeed("ip link >&2");
+      start_all()
+      machine.wait_for_unit("multi-user.target")
+      machine.succeed("ip link >&2")
     '';
 })
diff --git a/nixos/tests/leaps.nix b/nixos/tests/leaps.nix
index 6163fed56b6..65b475d734e 100644
--- a/nixos/tests/leaps.nix
+++ b/nixos/tests/leaps.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs,  ... }:
+import ./make-test-python.nix ({ pkgs,  ... }:
 
 {
   name = "leaps";
@@ -22,9 +22,11 @@ import ./make-test.nix ({ pkgs,  ... }:
 
   testScript =
     ''
-      startAll;
-      $server->waitForOpenPort(6666);
-      $client->waitForUnit("network.target");
-      $client->succeed("${pkgs.curl}/bin/curl http://server:6666/leaps/ | grep -i 'leaps'");
+      start_all()
+      server.wait_for_open_port(6666)
+      client.wait_for_unit("network.target")
+      assert "leaps" in client.succeed(
+          "${pkgs.curl}/bin/curl http://server:6666/leaps/"
+      )
     '';
 })
diff --git a/nixos/tests/lidarr.nix b/nixos/tests/lidarr.nix
index 85fcbd21d8c..d3f83e5d914 100644
--- a/nixos/tests/lidarr.nix
+++ b/nixos/tests/lidarr.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ lib, ... }:
+import ./make-test-python.nix ({ lib, ... }:
 
 with lib;
 
@@ -11,8 +11,10 @@ with lib;
     { services.lidarr.enable = true; };
 
   testScript = ''
-    $machine->waitForUnit('lidarr.service');
-    $machine->waitForOpenPort('8686');
-    $machine->succeed("curl --fail http://localhost:8686/");
+    start_all()
+
+    machine.wait_for_unit("lidarr.service")
+    machine.wait_for_open_port("8686")
+    machine.succeed("curl --fail http://localhost:8686/")
   '';
 })
diff --git a/nixos/tests/lightdm.nix b/nixos/tests/lightdm.nix
index ef30f7741e2..46c2ed7ccc5 100644
--- a/nixos/tests/lightdm.nix
+++ b/nixos/tests/lightdm.nix
@@ -8,9 +8,8 @@ import ./make-test-python.nix ({ pkgs, ...} : {
     imports = [ ./common/user-account.nix ];
     services.xserver.enable = true;
     services.xserver.displayManager.lightdm.enable = true;
-    services.xserver.windowManager.default = "icewm";
+    services.xserver.displayManager.defaultSession = "none+icewm";
     services.xserver.windowManager.icewm.enable = true;
-    services.xserver.desktopManager.default = "none";
   };
 
   enableOCR = true;
diff --git a/nixos/tests/mailcatcher.nix b/nixos/tests/mailcatcher.nix
index eb5b606ecc8..2ef38544fe0 100644
--- a/nixos/tests/mailcatcher.nix
+++ b/nixos/tests/mailcatcher.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ lib, ... }:
+import ./make-test-python.nix ({ lib, ... }:
 
 {
   name = "mailcatcher";
@@ -16,11 +16,15 @@ import ./make-test.nix ({ lib, ... }:
     };
 
   testScript = ''
-    startAll;
+    start_all()
 
-    $machine->waitForUnit('mailcatcher.service');
-    $machine->waitForOpenPort('1025');
-    $machine->succeed('echo "this is the body of the email" | mail -s "subject" root@example.org');
-    $machine->succeed('curl http://localhost:1080/messages/1.source') =~ /this is the body of the email/ or die;
+    machine.wait_for_unit("mailcatcher.service")
+    machine.wait_for_open_port("1025")
+    machine.succeed(
+        'echo "this is the body of the email" | mail -s "subject" root@example.org'
+    )
+    assert "this is the body of the email" in machine.succeed(
+        "curl http://localhost:1080/messages/1.source"
+    )
   '';
 })
diff --git a/nixos/tests/paperless.nix b/nixos/tests/paperless.nix
index 860ad0a6218..355e7041d3f 100644
--- a/nixos/tests/paperless.nix
+++ b/nixos/tests/paperless.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ lib, ... } : {
+import ./make-test-python.nix ({ lib, ... } : {
   name = "paperless";
   meta = with lib.maintainers; {
     maintainers = [ earvstedt ];
@@ -13,17 +13,24 @@ import ./make-test.nix ({ lib, ... } : {
   };
 
   testScript = ''
-    $machine->waitForUnit("paperless-consumer.service");
+    machine.wait_for_unit("paperless-consumer.service")
+
     # Create test doc
-    $machine->succeed('convert -size 400x40 xc:white -font "DejaVu-Sans" -pointsize 20 -fill black \
-      -annotate +5+20 "hello world 16-10-2005" /var/lib/paperless/consume/doc.png');
+    machine.succeed(
+        "convert -size 400x40 xc:white -font 'DejaVu-Sans' -pointsize 20 -fill black -annotate +5+20 'hello world 16-10-2005' /var/lib/paperless/consume/doc.png"
+    )
+
+    with subtest("Service gets ready"):
+        machine.wait_for_unit("paperless-server.service")
+        # Wait until server accepts connections
+        machine.wait_until_succeeds("curl -s localhost:28981")
 
-    $machine->waitForUnit("paperless-server.service");
-    # Wait until server accepts connections
-    $machine->waitUntilSucceeds("curl -s localhost:28981");
-    # Wait until document is consumed
-    $machine->waitUntilSucceeds('(($(curl -s localhost:28981/api/documents/ | jq .count) == 1))');
-    $machine->succeed("curl -s localhost:28981/api/documents/ | jq '.results | .[0] | .created'")
-      =~ /2005-10-16/ or die;
+    with subtest("Test document is consumed"):
+        machine.wait_until_succeeds(
+            "(($(curl -s localhost:28981/api/documents/ | jq .count) == 1))"
+        )
+        assert "2005-10-16" in machine.succeed(
+            "curl -s localhost:28981/api/documents/ | jq '.results | .[0] | .created'"
+        )
   '';
 })
diff --git a/nixos/tests/pdns-recursor.nix b/nixos/tests/pdns-recursor.nix
index bf6e6093d69..de1b60e0b1c 100644
--- a/nixos/tests/pdns-recursor.nix
+++ b/nixos/tests/pdns-recursor.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs, ... }: {
+import ./make-test-python.nix ({ pkgs, ... }: {
   name = "powerdns";
 
   nodes.server = { ... }: {
@@ -6,7 +6,7 @@ import ./make-test.nix ({ pkgs, ... }: {
   };
 
   testScript = ''
-    $server->waitForUnit("pdns-recursor");
-    $server->waitForOpenPort("53");
+    server.wait_for_unit("pdns-recursor")
+    server.wait_for_open_port("53")
   '';
 })
diff --git a/nixos/tests/peerflix.nix b/nixos/tests/peerflix.nix
index fae37fedaac..37628604d49 100644
--- a/nixos/tests/peerflix.nix
+++ b/nixos/tests/peerflix.nix
@@ -1,6 +1,6 @@
 # This test runs peerflix and checks if peerflix starts
 
-import ./make-test.nix ({ pkgs, ...} : {
+import ./make-test-python.nix ({ pkgs, ...} : {
   name = "peerflix";
   meta = with pkgs.stdenv.lib.maintainers; {
     maintainers = [ offline ];
@@ -15,9 +15,9 @@ import ./make-test.nix ({ pkgs, ...} : {
     };
 
   testScript = ''
-    startAll;
+    start_all()
 
-    $peerflix->waitForUnit("peerflix.service");
-    $peerflix->waitUntilSucceeds("curl localhost:9000");
+    peerflix.wait_for_unit("peerflix.service")
+    peerflix.wait_until_succeeds("curl localhost:9000")
   '';
 })
diff --git a/nixos/tests/pgmanage.nix b/nixos/tests/pgmanage.nix
index bacaf3f4158..4f5dbed24a9 100644
--- a/nixos/tests/pgmanage.nix
+++ b/nixos/tests/pgmanage.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs, ... } :
+import ./make-test-python.nix ({ pkgs, ... } :
 let
   role     = "test";
   password = "secret";
@@ -29,11 +29,13 @@ in
   };
 
   testScript = ''
-    startAll;
-    $one->waitForUnit("default.target");
-    $one->requireActiveUnit("pgmanage.service");
+    start_all()
+    one.wait_for_unit("default.target")
+    one.require_unit_state("pgmanage.service", "active")
 
     # Test if we can log in.
-    $one->waitUntilSucceeds("curl 'http://localhost:8080/pgmanage/auth' --data 'action=login&connname=${conn}&username=${role}&password=${password}' --fail");
+    one.wait_until_succeeds(
+        "curl 'http://localhost:8080/pgmanage/auth' --data 'action=login&connname=${conn}&username=${role}&password=${password}' --fail"
+    )
   '';
 })
diff --git a/nixos/tests/php-pcre.nix b/nixos/tests/php-pcre.nix
index ae44aec7944..d5c22e0582a 100644
--- a/nixos/tests/php-pcre.nix
+++ b/nixos/tests/php-pcre.nix
@@ -1,7 +1,7 @@
 
 let testString = "can-use-subgroups"; in
 
-import ./make-test.nix ({ ...}: {
+import ./make-test-python.nix ({ ...}: {
   name = "php-httpd-pcre-jit-test";
   machine = { lib, pkgs, ... }: {
     time.timeZone = "UTC";
@@ -31,9 +31,10 @@ import ./make-test.nix ({ ...}: {
   };
   testScript = { ... }:
   ''
-    $machine->waitForUnit('httpd.service');
+    machine.wait_for_unit("httpd.service")
     # Ensure php evaluation by matching on the var_dump syntax
-    $machine->succeed('curl -vvv -s http://127.0.0.1:80/index.php \
-      | grep "string(${toString (builtins.stringLength testString)}) \"${testString}\""');
+    assert 'string(${toString (builtins.stringLength testString)}) "${testString}"' in machine.succeed(
+        "curl -vvv -s http://127.0.0.1:80/index.php"
+    )
   '';
 })
diff --git a/nixos/tests/plasma5.nix b/nixos/tests/plasma5.nix
index 6884f17aabb..2eccfdf47f5 100644
--- a/nixos/tests/plasma5.nix
+++ b/nixos/tests/plasma5.nix
@@ -12,8 +12,8 @@ import ./make-test-python.nix ({ pkgs, ...} :
     imports = [ ./common/user-account.nix ];
     services.xserver.enable = true;
     services.xserver.displayManager.sddm.enable = true;
+    services.xserver.displayManager.defaultSession = "plasma5";
     services.xserver.desktopManager.plasma5.enable = true;
-    services.xserver.desktopManager.default = "plasma5";
     services.xserver.displayManager.sddm.autoLogin = {
       enable = true;
       user = "alice";
diff --git a/nixos/tests/postgis.nix b/nixos/tests/postgis.nix
index 294eb50b5fe..84bbb0bc8ec 100644
--- a/nixos/tests/postgis.nix
+++ b/nixos/tests/postgis.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ pkgs, ...} : {
+import ./make-test-python.nix ({ pkgs, ...} : {
   name = "postgis";
   meta = with pkgs.stdenv.lib.maintainers; {
     maintainers = [ lsix ];
@@ -20,10 +20,10 @@ import ./make-test.nix ({ pkgs, ...} : {
   };
 
   testScript = ''
-    startAll;
-    $master->waitForUnit("postgresql");
-    $master->sleep(10); # Hopefully this is long enough!!
-    $master->succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis;'");
-    $master->succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis_topology;'");
+    start_all()
+    master.wait_for_unit("postgresql")
+    master.sleep(10)  # Hopefully this is long enough!!
+    master.succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis;'")
+    master.succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis_topology;'")
   '';
 })
diff --git a/nixos/tests/quagga.nix b/nixos/tests/quagga.nix
index 6aee7ea57f0..04590aa0eb3 100644
--- a/nixos/tests/quagga.nix
+++ b/nixos/tests/quagga.nix
@@ -5,7 +5,7 @@
 #
 # All interfaces are in OSPF Area 0.
 
-import ./make-test.nix ({ pkgs, ... }:
+import ./make-test-python.nix ({ pkgs, ... }:
   let
 
     ifAddr = node: iface: (pkgs.lib.head node.config.networking.interfaces.${iface}.ipv4.addresses).address;
@@ -74,23 +74,23 @@ import ./make-test.nix ({ pkgs, ... }:
       testScript =
         { ... }:
         ''
-          startAll;
+          start_all()
 
           # Wait for the networking to start on all machines
-          $_->waitForUnit("network.target") foreach values %vms;
+          for machine in client, router1, router2, server:
+              machine.wait_for_unit("network.target")
 
-          # Wait for OSPF to form adjacencies
-          for my $gw ($router1, $router2) {
-              $gw->waitForUnit("ospfd");
-              $gw->waitUntilSucceeds("vtysh -c 'show ip ospf neighbor' | grep Full");
-              $gw->waitUntilSucceeds("vtysh -c 'show ip route' | grep '^O>'");
-          }
+          with subtest("Wait for OSPF to form adjacencies"):
+              for gw in router1, router2:
+                  gw.wait_for_unit("ospfd")
+                  gw.wait_until_succeeds("vtysh -c 'show ip ospf neighbor' | grep Full")
+                  gw.wait_until_succeeds("vtysh -c 'show ip route' | grep '^O>'")
 
-          # Test ICMP.
-          $client->succeed("ping -c 3 server >&2");
+          with subtest("Test ICMP"):
+              client.wait_until_succeeds("ping -c 3 server >&2")
 
-          # Test whether HTTP works.
-          $server->waitForUnit("httpd");
-          $client->succeed("curl --fail http://server/ >&2");
+          with subtest("Test whether HTTP works"):
+              server.wait_for_unit("httpd")
+              client.succeed("curl --fail http://server/ >&2")
         '';
     })
diff --git a/nixos/tests/sddm.nix b/nixos/tests/sddm.nix
index 4bdcd701dcf..a145705250f 100644
--- a/nixos/tests/sddm.nix
+++ b/nixos/tests/sddm.nix
@@ -16,9 +16,8 @@ let
         imports = [ ./common/user-account.nix ];
         services.xserver.enable = true;
         services.xserver.displayManager.sddm.enable = true;
-        services.xserver.windowManager.default = "icewm";
+        services.xserver.displayManager.defaultSession = "none+icewm";
         services.xserver.windowManager.icewm.enable = true;
-        services.xserver.desktopManager.default = "none";
       };
 
       enableOCR = true;
@@ -52,9 +51,8 @@ let
             user = "alice";
           };
         };
-        services.xserver.windowManager.default = "icewm";
+        services.xserver.displayManager.defaultSession = "none+icewm";
         services.xserver.windowManager.icewm.enable = true;
-        services.xserver.desktopManager.default = "none";
       };
 
       testScript = { nodes, ... }: let
diff --git a/nixos/tests/sonarr.nix b/nixos/tests/sonarr.nix
index 3e84445099a..764a4d05b38 100644
--- a/nixos/tests/sonarr.nix
+++ b/nixos/tests/sonarr.nix
@@ -1,4 +1,4 @@
-import ./make-test.nix ({ lib, ... }:
+import ./make-test-python.nix ({ lib, ... }:
 
 with lib;
 
@@ -11,8 +11,8 @@ with lib;
     { services.sonarr.enable = true; };
 
   testScript = ''
-    $machine->waitForUnit('sonarr.service');
-    $machine->waitForOpenPort('8989');
-    $machine->succeed("curl --fail http://localhost:8989/");
+    machine.wait_for_unit("sonarr.service")
+    machine.wait_for_open_port("8989")
+    machine.succeed("curl --fail http://localhost:8989/")
   '';
 })
diff --git a/nixos/tests/switch-test.nix b/nixos/tests/switch-test.nix
index 0dba3697980..7076bd77b77 100644
--- a/nixos/tests/switch-test.nix
+++ b/nixos/tests/switch-test.nix
@@ -1,6 +1,6 @@
 # Test configuration switching.
 
-import ./make-test.nix ({ pkgs, ...} : {
+import ./make-test-python.nix ({ pkgs, ...} : {
   name = "switch-test";
   meta = with pkgs.stdenv.lib.maintainers; {
     maintainers = [ gleber ];
@@ -28,7 +28,11 @@ import ./make-test.nix ({ pkgs, ...} : {
       exec env -i "$@" | tee /dev/stderr
     '';
   in ''
-    $machine->succeed("${stderrRunner} ${originalSystem}/bin/switch-to-configuration test");
-    $machine->succeed("${stderrRunner} ${otherSystem}/bin/switch-to-configuration test");
+    machine.succeed(
+        "${stderrRunner} ${originalSystem}/bin/switch-to-configuration test"
+    )
+    machine.succeed(
+        "${stderrRunner} ${otherSystem}/bin/switch-to-configuration test"
+    )
   '';
 })
diff --git a/nixos/tests/systemd-timesyncd.nix b/nixos/tests/systemd-timesyncd.nix
index d12b8eb2bf7..ad5b9a47383 100644
--- a/nixos/tests/systemd-timesyncd.nix
+++ b/nixos/tests/systemd-timesyncd.nix
@@ -1,7 +1,7 @@
 # Regression test for systemd-timesync having moved the state directory without
 # upstream providing a migration path. https://github.com/systemd/systemd/issues/12131
 
-import ./make-test.nix (let
+import ./make-test-python.nix (let
   common = { lib, ... }: {
     # override the `false` value from the qemu-vm base profile
     services.timesyncd.enable = lib.mkForce true;
@@ -25,28 +25,28 @@ in {
   };
 
   testScript = ''
-    startAll;
-    $current->succeed('systemctl status systemd-timesyncd.service');
+    start_all()
+    current.succeed("systemctl status systemd-timesyncd.service")
     # on a new install with a recent systemd there should not be any
     # leftovers from the dynamic user mess
-    $current->succeed('test -e /var/lib/systemd/timesync');
-    $current->succeed('test ! -L /var/lib/systemd/timesync');
+    current.succeed("test -e /var/lib/systemd/timesync")
+    current.succeed("test ! -L /var/lib/systemd/timesync")
 
     # timesyncd should be running on the upgrading system since we fixed the
     # file bits in the activation script
-    $pre1909->succeed('systemctl status systemd-timesyncd.service');
+    pre1909.succeed("systemctl status systemd-timesyncd.service")
 
     # the path should be gone after the migration
-    $pre1909->succeed('test ! -e /var/lib/private/systemd/timesync');
+    pre1909.succeed("test ! -e /var/lib/private/systemd/timesync")
 
     # and the new path should no longer be a symlink
-    $pre1909->succeed('test -e /var/lib/systemd/timesync');
-    $pre1909->succeed('test ! -L /var/lib/systemd/timesync');
+    pre1909.succeed("test -e /var/lib/systemd/timesync")
+    pre1909.succeed("test ! -L /var/lib/systemd/timesync")
 
     # after a restart things should still work and not fail in the activation
     # scripts and cause the boot to fail..
-    $pre1909->shutdown;
-    $pre1909->start;
-    $pre1909->succeed('systemctl status systemd-timesyncd.service');
+    pre1909.shutdown()
+    pre1909.start()
+    pre1909.succeed("systemctl status systemd-timesyncd.service")
   '';
 })
diff --git a/nixos/tests/wireguard/namespaces.nix b/nixos/tests/wireguard/namespaces.nix
index 94f993d9475..c8a4e3bb52a 100644
--- a/nixos/tests/wireguard/namespaces.nix
+++ b/nixos/tests/wireguard/namespaces.nix
@@ -13,7 +13,7 @@ let
 
 in
 
-import ../make-test.nix ({ pkgs, ...} : {
+import ../make-test-python.nix ({ pkgs, ...} : {
   name = "wireguard-with-namespaces";
   meta = with pkgs.stdenv.lib.maintainers; {
     maintainers = [ asymmetric ];
@@ -65,16 +65,14 @@ import ../make-test.nix ({ pkgs, ...} : {
   };
 
   testScript = ''
-    startAll();
+    start_all()
 
-    $peer0->waitForUnit("wireguard-wg0.service");
-    $peer1->waitForUnit("wireguard-wg0.service");
-    $peer2->waitForUnit("wireguard-wg0.service");
-    $peer3->waitForUnit("wireguard-wg0.service");
+    for machine in peer0, peer1, peer2, peer3:
+        machine.wait_for_unit("wireguard-wg0.service")
 
-    $peer0->succeed("ip -n ${socketNamespace} link show wg0");
-    $peer1->succeed("ip -n ${interfaceNamespace} link show wg0");
-    $peer2->succeed("ip -n ${interfaceNamespace} link show wg0");
-    $peer3->succeed("ip link show wg0");
+    peer0.succeed("ip -n ${socketNamespace} link show wg0")
+    peer1.succeed("ip -n ${interfaceNamespace} link show wg0")
+    peer2.succeed("ip -n ${interfaceNamespace} link show wg0")
+    peer3.succeed("ip link show wg0")
   '';
 })
diff --git a/nixos/tests/xmonad.nix b/nixos/tests/xmonad.nix
index ab3888ca43f..ef711f8dcf6 100644
--- a/nixos/tests/xmonad.nix
+++ b/nixos/tests/xmonad.nix
@@ -4,10 +4,10 @@ import ./make-test-python.nix ({ pkgs, ...} : {
     maintainers = [ nequissimus ];
   };
 
-  machine = { lib, pkgs, ... }: {
+  machine = { pkgs, ... }: {
     imports = [ ./common/x11.nix ./common/user-account.nix ];
     services.xserver.displayManager.auto.user = "alice";
-    services.xserver.windowManager.default = lib.mkForce "xmonad";
+    services.xserver.displayManager.defaultSession = "none+xmonad";
     services.xserver.windowManager.xmonad = {
       enable = true;
       enableContribAndExtras = true;