melpa-packages: build osx-dictionary helper executable

The `osx-dictionary` emacs package tries to build a helper executable
if it is not found at runtime. This fails with `nix` installations of
the package, so we build it at build time.

pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix

@@ -688,6 +688,27 @@ let
               --replace '"mozc_emacs_helper"' '"${pkgs.ibus-engines.mozc}/lib/mozc/mozc_emacs_helper"'
           '';
         });
+
+        # Build a helper executable that interacts with the macOS Dictionary.app
+        osx-dictionary =
+          if pkgs.stdenv.isDarwin
+          then super.osx-dictionary.overrideAttrs (old: {
+            buildInputs =
+              old.buildInputs ++
+              (with pkgs.darwin.apple_sdk.frameworks; [CoreServices Foundation]);
+            dontUnpack = false;
+            buildPhase = (old.buildPhase or "") + ''
+              cd source
+              $CXX -O3 -framework CoreServices -framework Foundation osx-dictionary.m -o osx-dictionary-cli
+            '';
+            postInstall = (old.postInstall or "") + "\n" + ''
+              outd=$out/share/emacs/site-lisp/elpa/osx-dictionary-*
+              mkdir -p $out/bin
+              install -m444 -t $out/bin osx-dictionary-cli
+              rm $outd/osx-dictionary.m
+            '';
+          })
+          else super.osx-dictionary;
       };
 
     in lib.mapAttrs (n: v: if lib.hasAttr n overrides then overrides.${n} else v) super);