key-mapper: Hack the derivation path more cleanly

packages/key-mapper/default.nix

@@ -1,4 +1,4 @@
-{ pkgs, lib, python3Packages, python3, gtk3, gobject-introspection, git, wrapGAppsHook, gnome }:
+{ pkgs, lib, python3Packages, python3, gtk3, gobject-introspection, git, wrapGAppsHook, gnome, makeDesktopItem }:
 
 python3Packages.buildPythonApplication rec {
   pname = "key-mapper";
@@ -23,6 +23,11 @@ python3Packages.buildPythonApplication rec {
     ./hack-data-dir.patch
   ];
 
+  # Fix keymapper not finding its data files
+  preBuild = ''
+    sed -e "s|NIXOS_OUT_PATH|$out/usr/share/key-mapper|" --in-place keymapper/data.py
+  '';
+  
   # Required as we otherwise don't get the dbus policy installed
   # correctly
   preInstall = ''
@@ -30,6 +35,14 @@ python3Packages.buildPythonApplication rec {
     ${python3}/bin/${python3.executable} setup.py install_data --install-dir=$out --root=$out
   '';
 
+  desktopItem = makeDesktopItem {
+    name = "key-mapper";
+    exec = "$out/bin/key-mapper-gtk";
+    icon = "$out/usr/share/key-mapper/key-mapper.svg";
+    desktopName = "key-mapper";
+    genericName = "key-mapper";
+  };
+  
   meta = with lib; {
     homepage = "https://github.com/sezanzeb/key-mapper";
     description = "A tool to change the mapping of your input device buttons";

packages/key-mapper/hack-data-dir.patch

@@ -1,12 +1,12 @@
 diff --git a/keymapper/data.py b/keymapper/data.py
-index d909399..f7716ac 100644
+index d909399..7e4aad0 100644
 --- a/keymapper/data.py
 +++ b/keymapper/data.py
 @@ -68,6 +68,7 @@ def get_data_path(filename=''):
          '/usr/share/key-mapper',
          '/usr/local/share/key-mapper',
          os.path.join(site.USER_BASE, 'share/key-mapper'),
-+        os.environ["KEYMAPPER_DATA"],
++        'NIXOS_OUT_PATH',
      ]
  
      if data is None: