chore(lib): fix for a new version of nixpkgs

NixOS/nixpkgs@062945b

modules/lib/default.nix

@@ -133,8 +133,15 @@ in
   # a -> a -> a
   # see https://nlewo.github.io/nixos-manual-sphinx/development/option-types.xml.html
   # by default enums cannot be merged, but they keep their passed value in `functor.payload`.
-  # `functor.binOp` can merge those values
-  mergeEnums = a: b: lib.types.enum (a.functor.binOp a.functor.payload b.functor.payload);
+  # (or `functor.payload.values` on unstable) `functor.binOp` can merge those values
+  mergeEnums =
+    a: b:
+    let
+      result = a.functor.binOp a.functor.payload b.functor.payload;
+      # see https://github.com/NixOS/nixpkgs/commit/062945b725875167a24b11c4c1f2ba8e7623d3d6
+      values = if builtins.typeOf result == "set" then result.values else result;
+    in
+    lib.types.enum values;
 
   # string
   # returns the current release version of nixos or home-manager. throws an evaluation error if neither are