gnome3.gnome-settings-daemon: fix #14168

The issue in brief is caused by the fact that gnome-settings-daemon is
non-restartable and if the policy definitions change in any way
it won't propagate to the running system because of that.

By patching references to the backlight helper to
/run/current-system/sw/bin/gsd-backlight-helper
the polkit policy will not undergo a change.

pkgs/desktops/gnome-3/core/gnome-settings-daemon/default.nix

@@ -50,6 +50,7 @@ stdenv.mkDerivation rec {
       src = ./fix-paths.patch;
       inherit tzdata;
     })
+    ./global-backlight-helper.patch
   ];
 
   nativeBuildInputs = [
@@ -93,6 +94,12 @@ stdenv.mkDerivation rec {
     "-Dudev_dir=${placeholder "out"}/lib/udev"
   ];
 
+  # So the polkit policy can reference /run/current-system/sw/bin/gnome-settings-daemon/gsd-backlight-helper
+  postFixup = ''
+    mkdir -p $out/bin/gnome-settings-daemon
+    ln -s $out/libexec/gsd-backlight-helper $out/bin/gnome-settings-daemon/gsd-backlight-helper
+  '';
+
   postPatch = ''
     for f in gnome-settings-daemon/codegen.py plugins/power/gsd-power-constants-update.pl meson_post_install.py; do
       chmod +x $f

pkgs/desktops/gnome-3/core/gnome-settings-daemon/global-backlight-helper.patch

@@ -0,0 +1,26 @@
+diff --git a/plugins/power/gsd-backlight.c b/plugins/power/gsd-backlight.c
+index d7d10fd2..5619d6ad 100644
+--- a/plugins/power/gsd-backlight.c
++++ b/plugins/power/gsd-backlight.c
+@@ -358,7 +358,7 @@ gsd_backlight_run_set_helper (GsdBacklight *backlight, GTask *task)
+                 proc = g_subprocess_new (G_SUBPROCESS_FLAGS_STDOUT_SILENCE,
+                                          &error,
+                                          "pkexec",
+-                                         LIBEXECDIR "/gsd-backlight-helper",
++                                         "/run/current-system/sw/bin/gnome-settings-daemon/gsd-backlight-helper",
+                                          g_udev_device_get_sysfs_path (backlight->udev_device),
+                                          data->value_str, NULL);
+         } else {
+diff --git a/plugins/power/org.gnome.settings-daemon.plugins.power.policy.in.in b/plugins/power/org.gnome.settings-daemon.plugins.power.policy.in.in
+index f16300f8..79d6bd17 100644
+--- a/plugins/power/org.gnome.settings-daemon.plugins.power.policy.in.in
++++ b/plugins/power/org.gnome.settings-daemon.plugins.power.policy.in.in
+@@ -25,7 +25,7 @@
+       <allow_inactive>no</allow_inactive>
+       <allow_active>yes</allow_active>
+     </defaults>
+-    <annotate key="org.freedesktop.policykit.exec.path">@libexecdir@/gsd-backlight-helper</annotate>
++    <annotate key="org.freedesktop.policykit.exec.path">/run/current-system/sw/bin/gnome-settings-daemon/gsd-backlight-helper</annotate>
+   </action>
+
+ </policyconfig>