nixos/programs/gnome-session: add top-level systemd namespace for systemd-specific options

Also included a little refactor.

modules/nixos/programs/gnome-session/default.nix

@@ -107,20 +107,20 @@ let
           pathToUnit serviceToUnit targetToUnit timerToUnit socketToUnit;
 
         mkSystemdUnits = name: component: {
-          "${component.id}.service" = serviceToUnit component.serviceUnit;
-          "${component.id}.target" = targetToUnit component.targetUnit;
-        } // lib.optionalAttrs (component.socketUnit != null) {
-          "${component.id}.socket" = socketToUnit component.socketUnit;
-        } // lib.optionalAttrs (component.timerUnit != null) {
-          "${component.id}.timer" = timerToUnit component.timerUnit;
-        } // lib.optionalAttrs (component.pathUnit != null) {
-          "${component.id}.path" = pathToUnit component.pathUnit;
+          "${component.id}.service" = serviceToUnit component.systemd.serviceUnit;
+          "${component.id}.target" = targetToUnit component.systemd.targetUnit;
+        } // lib.optionalAttrs (component.systemd.socketUnit != null) {
+          "${component.id}.socket" = socketToUnit component.systemd.socketUnit;
+        } // lib.optionalAttrs (component.systemd.timerUnit != null) {
+          "${component.id}.timer" = timerToUnit component.systemd.timerUnit;
+        } // lib.optionalAttrs (component.systemd.pathUnit != null) {
+          "${component.id}.path" = pathToUnit component.systemd.pathUnit;
         };
 
         componentsUnits = lib.concatMapAttrs mkSystemdUnits session.components;
       in
       componentsUnits // {
-        "gnome-session@${session.name}.target" = targetToUnit session.targetUnit;
+        "gnome-session@${session.name}.target" = targetToUnit session.systemd.targetUnit;
       }
     )
     cfg.sessions;

modules/nixos/programs/gnome-session/submodules/component-type.nix

@@ -1,10 +1,13 @@
 { name, config, pkgs, lib, utils, session, ... }:
 
 let
-  optionalSystemdUnitOption = type: systemdModuleAttribute:
+  optionalSystemdUnitOption = {
+    unitType, systemdModuleAttribute, otherType,
+  }:
     lib.mkOption {
+      type = lib.types.nullOr otherType;
       description = ''
-        An optional systemd ${type} configuration to be generated. This should
+        An optional systemd ${unitType} configuration to be generated. This should
         be configured if the session is managed by systemd.
 
         :::{.note}
@@ -73,6 +76,7 @@ in
       };
     };
 
+    systemd = {
       # Most of the systemd config types are trying to eliminate as much of the
       # NixOS systemd extensions as much as possible. For more details, see
       # `config` attribute of the `sessionType`.
@@ -136,43 +140,50 @@ in
         visible = "shallow";
       };
 
-    timerUnit = optionalSystemdUnitOption "timer" "timers" // {
-      type =
+      timerUnit = optionalSystemdUnitOption {
+        unitType = "timer";
+        systemdModuleAttribute = "timers";
+        otherType =
           let
             inherit (utils.systemdUtils.unitOptions) timerOptions commonUnitOptions;
             inherit (utils.systemdUtils.lib) unitConfig;
           in
-        with lib.types; nullOr (submodule [
+          lib.types.submodule [
             commonUnitOptions
             timerOptions
             unitConfig
-        ]);
+          ];
       };
 
-    socketUnit = optionalSystemdUnitOption "socket" "sockets" // {
-      type =
+      socketUnit = optionalSystemdUnitOption {
+        unitType = "socket";
+        systemdModuleAttribute = "sockets";
+        otherType =
           let
             inherit (utils.systemdUtils.unitOptions) socketOptions commonUnitOptions;
             inherit (utils.systemdUtils.lib) unitConfig;
           in
-        with lib.types; nullOr (submodule [
+          lib.types.submodule [
             commonUnitOptions
             socketOptions
             unitConfig
-        ]);
+          ];
       };
 
-    pathUnit = optionalSystemdUnitOption "path" "paths" // {
-      type =
+      pathUnit = optionalSystemdUnitOption {
+        unitType = "path";
+        systemdModuleAttribute = "paths";
+        otherType =
           let
             inherit (utils.systemdUtils.unitOptions) pathOptions commonUnitOptions;
             inherit (utils.systemdUtils.lib) unitConfig;
           in
-        with lib.types; nullOr (submodule [
+          lib.types.submodule [
             commonUnitOptions
             pathOptions
             unitConfig
-        ]);
+          ];
+      };
     };
 
     id = lib.mkOption {
@@ -235,7 +246,7 @@ in
       systemd user unit, much of them are unnecessary and rarely needed (if
       ever like `Service.PrivateTmp=`?) so we didn't set such defaults here.
     */
-    serviceUnit = {
+    systemd.serviceUnit = {
       script = lib.mkAfter config.script;
       description = lib.mkDefault config.description;
 
@@ -282,7 +293,7 @@ in
       likely for a user to design their own desktop session with full control
       so it would be better for these options to be empty for less confusion.
     */
-    targetUnit = {
+    systemd.targetUnit = {
       # This should be the dependency-related directive to be configured. The
       # rest is for the user to judge.
       wants = [ "${config.id}.service" ];

modules/nixos/programs/gnome-session/submodules/session-type.nix

@@ -184,6 +184,7 @@ in
       ];
     };
 
+    systemd = {
       targetUnit = lib.mkOption {
         type =
           let
@@ -220,12 +221,13 @@ in
         '';
       };
     };
+  };
 
   config = {
     # Append the session argument.
     extraArgs = [ "--session=${name}" ];
 
-    targetUnit = {
+    systemd.targetUnit = {
       overrideStrategy = lib.mkForce "asDropin";
       wants = lib.mkDefault (builtins.map (c: "${c}.target") config.requiredComponents);
     };