pantheon.elementary-greeter: hardcode fallback wallpaper

Workaround https://github.com/elementary/greeter/issues/360

pkgs/desktops/pantheon/desktop/elementary-greeter/default.nix

@@ -1,6 +1,7 @@
 { stdenv
 , fetchFromGitHub
 , linkFarm
+, substituteAll
 , elementary-greeter
 , pantheon
 , pkgconfig
@@ -86,6 +87,11 @@ stdenv.mkDerivation rec {
 
   patches = [
     ./sysconfdir-install.patch
+    # Needed until https://github.com/elementary/greeter/issues/360 is fixed
+    (substituteAll {
+      src = ./hardcode-fallback-background.patch;
+      default_wallpaper = "${nixos-artwork.wallpapers.simple-dark-gray}/share/artwork/gnome/nix-wallpaper-simple-dark-gray.png";
+    })
   ];
 
   preFixup = ''

pkgs/desktops/pantheon/desktop/elementary-greeter/hardcode-fallback-background.patch

@@ -0,0 +1,22 @@
+diff --git a/src/Cards/BackgroundImage.vala b/src/Cards/BackgroundImage.vala
+index b57fb4d..ddfd56c 100644
+--- a/src/Cards/BackgroundImage.vala
++++ b/src/Cards/BackgroundImage.vala
+@@ -9,7 +9,7 @@ public class Greeter.BackgroundImage : Gtk.EventBox {
+ 
+     public BackgroundImage (string? path) {
+         if (path == null) {
+-            path = "/usr/share/backgrounds/elementaryos-default";
++            path = "@default_wallpaper@";
+         }
+ 
+         try {
+@@ -19,7 +19,7 @@ public class Greeter.BackgroundImage : Gtk.EventBox {
+             critical ("Fallback to default wallpaper");
+ 
+             try {
+-                full_pixbuf = new Gdk.Pixbuf.from_file ("/usr/share/backgrounds/elementaryos-default");
++                full_pixbuf = new Gdk.Pixbuf.from_file ("@default_wallpaper");
+             } catch (GLib.Error e) {
+                 critical (e.message);
+             }