geoclue2 service: add option to run demo agent

nixos/modules/services/desktops/geoclue2.nix

@@ -4,6 +4,10 @@
 
 with lib;
 
+let
+  # the demo agent isn't built by default, but we need it here
+  package = pkgs.geoclue2.override { withDemoAgent = config.services.geoclue2.enableDemoAgent; };
+in
 {
 
   ###### interface
@@ -21,21 +25,42 @@ with lib;
         '';
       };
 
+      enableDemoAgent = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Whether to use the GeoClue demo agent. This should be
+          overridden by desktop environments that provide their own
+          agent.
+        '';
+      };
+
     };
 
   };
 
 
   ###### implementation
-
   config = mkIf config.services.geoclue2.enable {
 
-    environment.systemPackages = [ pkgs.geoclue2 ];
-
-    services.dbus.packages = [ pkgs.geoclue2 ];
-
-    systemd.packages = [ pkgs.geoclue2 ];
-
+    environment.systemPackages = [ package ];
+
+    services.dbus.packages = [ package ];
+
+    systemd.packages = [ package ];
+
+    # this needs to run as a user service, since it's associated with the
+    # user who is making the requests
+    systemd.user.services = mkIf config.services.geoclue2.enableDemoAgent { 
+      "geoclue-agent" = {
+        description = "Geoclue agent";
+        script = "${package}/libexec/geoclue-2.0/demos/agent";
+        # this should really be `partOf = [ "geoclue.service" ]`, but
+        # we can't be part of a system service, and the agent should
+        # be okay with the main service coming and going
+        wantedBy = [ "default.target" ];
+      };
+    };
   };
 
 }

nixos/modules/services/x11/desktop-managers/gnome3.nix

@@ -93,6 +93,8 @@ in {
     services.udisks2.enable = true;
     services.accounts-daemon.enable = true;
     services.geoclue2.enable = mkDefault true;
+    # GNOME should have its own geoclue agent
+    services.geoclue2.enableDemoAgent = false;
     services.dleyna-renderer.enable = mkDefault true;
     services.dleyna-server.enable = mkDefault true;
     services.gnome3.at-spi2-core.enable = true;