nixos/automatic-timezoned: set time.timeZone to null to avoid silent overriding (#347217)

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -685,6 +685,9 @@
 
 - ZFS now imports its pools in `postResumeCommands` rather than `postDeviceCommands`. If you had `postDeviceCommands` scripts that depended on ZFS pools being imported, those now need to be in `postResumeCommands`.
 
+- `services.automatic-timezoned.enable = true` will now set `time.timeZone = null`.
+  This is to avoid silently shadowing a user's explicitly defined timezone without recognition on the user's part.
+
 - `services.localtimed.enable = true` will now set `time.timeZone = null`.
   This is to avoid silently shadowing a user's explicitly defined timezone without recognition on the user's part.
 

nixos/modules/services/system/automatic-timezoned.nix

@@ -16,6 +16,11 @@ in
           timezone up-to-date based on the current location. It uses geoclue2 to
           determine the current location and systemd-timedated to actually set
           the timezone.
+
+          To avoid silent overriding by the service, if you have explicitly set a
+          timezone, either remove it or ensure that it is set with a lower priority
+          than the default value using `lib.mkDefault` or `lib.mkOverride`. This is
+          to make the choice deliberate. An error will be presented otherwise.
         '';
       };
       package = mkPackageOption pkgs "automatic-timezoned" { };
@@ -23,6 +28,10 @@ in
   };
 
   config = mkIf cfg.enable {
+    # This will give users an error if they have set an explicit time
+    # zone, rather than having the service silently override it.
+    time.timeZone = null;
+
     security.polkit.extraConfig = ''
       polkit.addRule(function(action, subject) {
         if (action.id == "org.freedesktop.timedate1.set-timezone"