nixos/programs/sessiond: refactor and update comments

modules/nixos/programs/sessiond/submodules/component-type.nix

@@ -1,4 +1,22 @@
-{ name, config, lib, session, utils, ... }: {
+{ name, config, lib, session, utils, ... }:
+
+let
+  optionalSystemdUnitOption = type: systemdModuleAttribute:
+    lib.mkOption {
+      description = ''
+        An optional systemd ${type} configuration to be generated.
+
+        :::{.note}
+        This has the same options as
+        {option}`systemd.user.${systemdModuleAttribute}.<name>` but without
+        certain options from stage 2 counterparts such as `reloadTriggers` and
+        `restartTriggers`.
+        :::
+      '';
+      default = null;
+    };
+in
+{
   options = {
     description = lib.mkOption {
       type = lib.types.nonEmptyStr;
@@ -31,14 +49,11 @@
         `reloadTriggers` and `restartTriggers`.
 
         By default, this module sets the service unit as part of the respective
-        target unit (i.e., `PartOf=$COMPONENTID.target`).
+        target unit (i.e., `PartOf=$COMPONENTID.target`). On a typical case,
-
+        you shouldn't mess with much of the dependency ordering with the
-        On a typical case, you shouldn't mess with much of the dependency
+        service unit. You should configure `targetUnit` for that instead.
-        ordering with the service unit. You should configure `targetUnit` for
-        that instead.
         :::
       '';
-      default = { };
     };
 
     targetUnit = lib.mkOption {
@@ -52,22 +67,19 @@
           unitConfig
         ];
       description = ''
-        systemd target configuration to be generated. This should be
+        systemd target configuration to be generated. This is generated by
-        configured if the session is managed by systemd.
+        default alongside the service where it is configured to be a part of
+        the target unit.
 
         :::{.note}
-        This is generated by default alongside the service where it is
-        configured to be a part of the target unit.
-
         This has the same options as {option}`systemd.user.targets.<name>`
         but without certain options from stage 2 counterparts such as
         `reloadTriggers` and `restartTriggers`.
         :::
       '';
-      default = { };
     };
 
-    timerUnit = lib.mkOption {
+    timerUnit = optionalSystemdUnitOption "timer" "timers" // {
       type =
         let
           inherit (utils.systemdUtils.unitOptions) timerOptions commonUnitOptions;
@@ -78,20 +90,9 @@
           timerOptions
           unitConfig
         ]);
-      description = ''
-        An optional systemd timer configuration to be generated. This should
-        be configured if the session is managed by systemd.
-
-        :::{.note}
-        This has the same options as {option}`systemd.user.timers.<name>`
-        but without certain options from stage 2 counterparts such as
-        `reloadTriggers` and `restartTriggers`.
-        :::
-      '';
-      default = null;
     };
 
-    socketUnit = lib.mkOption {
+    socketUnit = optionalSystemdUnitOption "socket" "sockets" // {
       type =
         let
           inherit (utils.systemdUtils.unitOptions) socketOptions commonUnitOptions;
@@ -102,20 +103,9 @@
           socketOptions
           unitConfig
         ]);
-      description = ''
-        An optional systemd socket configuration to be generated. This should
-        be configured if the session is managed by systemd.
-
-        :::{.note}
-        This has the same options as {option}`systemd.user.sockets.<name>`
-        but without certain options from stage 2 counterparts such as
-        `reloadTriggers` and `restartTriggers`.
-        :::
-      '';
-      default = null;
     };
 
-    pathUnit = lib.mkOption {
+    pathUnit = optionalSystemdUnitOption "path" "paths" // {
       type =
         let
           inherit (utils.systemdUtils.unitOptions) pathOptions commonUnitOptions;
@@ -126,17 +116,6 @@
           pathOptions
           unitConfig
         ]);
-      description = ''
-        An optional systemd path configuration to be generated. This should
-        be configured if the session is managed by systemd.
-
-        :::{.note}
-        This has the same options as {option}`systemd.user.paths.<name>`
-        but without certain options from stage 2 counterparts such as
-        `reloadTriggers` and `restartTriggers`.
-        :::
-      '';
-      default = null;
     };
 
     id = lib.mkOption {
@@ -163,26 +142,12 @@
       know how different desktop components interact with each other
       especially if one of them failed.
 
-      TODO: Is `Type=notify` a good default?
-      * `Service.Type=` is obviously not included since not all desktop
-      components are the same either. Some of them could a D-Bus service,
-      some of them are oneshots, etc. Not to mention, this is already implied
-      to be `Type=simple` by systemd anyways.
-
       * `Service.OOMScoreAdjust=` have different values for different
       components so it isn't included.
 
       * Most sandboxing options. Aside from the fact we're dealing with a
       systemd user unit, much of them are unnecessary and rarely needed (if
       ever like `Service.PrivateTmp=`?) so we didn't set such defaults here.
-
-      As you can tell, this module does not provide a framework for the user
-      to easily compose their own desktop environment. THIS MODULE ALREADY
-      DOES A LOT, ALRIGHT! CUT ME SOME SLACK!
-
-      Take note that the default service configuration is leaning on the
-      desktop component being a simple type of service like how most NixOS
-      service modules are deployed.
     */
     serviceUnit = {
       description = lib.mkDefault config.description;
@@ -211,14 +176,8 @@
     };
 
     /*
-      Similarly, there are things that COULD make it here but didn't for a
+      Take note the session target unit already has `Wants=$COMPONENT.target`
-      variety of reasons.
+      so no need to set dependency ordering directives here.
-
-      * `Unit.PartOf=`, `Unit.Requisite=`, and the like since some components
-      require starting up earlier than the others. We could include it here
-      if we make it clear in the documentation or if it proves to be a
-      painful experience to configure this by a first-timer. For now, this is
-      on the user to know.
     */
     targetUnit = {
       wants = [ "${config.id}.service" ];