mautrix-gmessages: add goolm override (#425622)

pkgs/by-name/ma/mautrix-gmessages/package.nix

@@ -6,6 +6,12 @@
   nix-update-script,
   testers,
   mautrix-gmessages,
+  # This option enables the use of an experimental pure-Go implementation of the
+  # Olm protocol instead of libolm for end-to-end encryption. Using goolm is not
+  # recommended by the mautrix developers, but they are interested in people
+  # trying it out in non-production-critical environments and reporting any
+  # issues they run into.
+  withGoolm ? false,
 }:
 
 buildGoModule rec {
@@ -28,7 +34,8 @@ buildGoModule rec {
     "main.Tag=${version}"
   ];
 
-  buildInputs = [ olm ];
+  buildInputs = lib.optional (!withGoolm) olm;
+  tags = lib.optional withGoolm "goolm";
 
   doCheck = false;