nixgl: make desktop files point to wrapped exe

Some desktop files will refer to the absolute path of the original
derivation, which would bypass nixGL wrapping. So we need to replace the
path with the path to the wrapper derivation to ensure the wrapped
version is always launched.

modules/misc/nixgl.nix

@@ -57,6 +57,17 @@ in {
               echo "exec -a \"\$0\" ${cfg.prefix} $file \"\$@\"" >> "$out/bin/$(basename $file)"
               chmod +x "$out/bin/$(basename $file)"
             done
+
+            # If .desktop files refer to the old package, replace the references
+            for dsk in "$out/share/applications"/*.desktop ; do
+              if ! grep "${pkg.out}" "$dsk" > /dev/null; then
+                continue
+              fi
+              src="$(readlink "$dsk")"
+              rm "$dsk"
+              sed "s|${pkg.out}|$out|g" "$src" > "$dsk"
+            done
+
             shopt -u nullglob # Revert nullglob back to its normal default state
           '';
         }));