emacs.pkgs.jabber: build with OMEMO support

Emacs-jabber requires a third-party picomemo library for OMEMO support.
It is not strictly required for package to function, but it is needed for E2EE chats.

Co-authored-by: Lin Jian <me@linj.tech>
Signed-off-by: Sergey Makarov <12733495+SeTSeR@users.noreply.github.com>

pkgs/applications/editors/emacs/elisp-packages/nongnu-common-overrides.nix

@@ -20,5 +20,22 @@ in
       yasnippet
     ]
   );
+
+  # requires optional dependency for OMEMO support.
+  jabber = super.jabber.overrideAttrs (old: {
+    buildInputs = old.buildInputs ++ [ pkgs.mbedtls ];
+    nativeBuildInputs = old.nativeBuildInputs ++ [ pkgs.pkg-config ];
+
+    # We need to run this in postInstall for package directory to become available
+    postInstall =
+      (old.postInstall or "")
+      + "\n"
+      + ''
+        pushd $out/share/emacs/site-lisp/elpa/jabber-*/src
+        make CC=$CC
+        rm -r $out/share/emacs/site-lisp/elpa/jabber-*/src
+        popd
+      '';
+  });
   # keep-sorted end
 }