redshift: install desktop files, and use absolute paths in them to avoid confusing geoclue agent

nixos/modules/services/x11/redshift.nix

@@ -116,6 +116,9 @@ in {
       }
     ];
 
+    # needed so that .desktop files are installed, which geoclue cares about
+    environment.systemPackages = [ cfg.package ];
+
     services.geoclue2.enable = mkIf (cfg.provider == "geoclue2") true;
 
     systemd.user.services.redshift = 

pkgs/applications/misc/redshift/default.nix

@@ -61,6 +61,15 @@ stdenv.mkDerivation rec {
 
   postFixup = "wrapPythonPrograms";
 
+  # the geoclue agent may inspect these paths and expect them to be
+  # valid without having the correct $PATH set
+  postInstall = ''
+    substituteInPlace $out/share/applications/redshift.desktop \
+      --replace 'Exec=redshift' "Exec=$out/bin/redshift"
+    substituteInPlace $out/share/applications/redshift.desktop \
+      --replace 'Exec=redshift-gtk' "Exec=$out/bin/redshift-gtk"
+  '';
+
   enableParallelBuilding = true;
 
   meta = with stdenv.lib; {