Add a desktop file for sm64ex.

nix/steam_deck/configuration/roles/sm64ex/default.nix

@@ -23,7 +23,7 @@
         allowedUnfree = [ "sm64ex" ];
 
         home.packages = with pkgs; [
-          (config.lib.nixGL.wrap sm64ex)
+          sm64ex
         ];
 
         # nixpkgs.overlays = [
@@ -43,6 +43,41 @@
             ".local/share/sm64ex/sm64_save_file.bin"
           ];
         };
+
+        nixpkgs.overlays = [
+          (final: prev: {
+            sm64ex =
+              let
+                desktop_item = pkgs.makeDesktopItem {
+                  name = "sm64ex";
+                  desktopName = "Super Mario 64";
+                  comment = "A PC Port of Super Mario 64.";
+                  categories = [
+                    "Game"
+                  ];
+                  icon = "sm64ex";
+                  type = "Application";
+                  exec = "sm64ex";
+                };
+              in
+              pkgs.buildEnv {
+                name = prev.sm64ex.name;
+                paths = [
+                  (config.lib.nixGL.wrap prev.sm64ex)
+                ];
+                extraOutputsToInstall = [
+                  "man"
+                  "doc"
+                  "info"
+                ];
+                # We have to use 555 instead of the normal 444 here because the .desktop file ends up inside $HOME on steam deck and desktop files must be either not in $HOME or must be executable, otherwise KDE Plasma refuses to execute them.
+                postBuild = ''
+                  install -m 555 -D "${desktop_item}/share/applications/"* -t $out/share/applications/
+                  install -m 444 -D "${./files/icon.png}" $out/share/pixmaps/sm64ex.png
+                '';
+              };
+          })
+        ];
       })
     ]
   );