Emit standalone lens pairs for nested record composition

record.ml

@@ -38,3 +38,17 @@ let () =
   (try ignore (Colour.update_red ~f:(fun _ -> failwith "callback") original); assert false
    with Failure message -> assert (message = "callback"));
   assert (Colour.red original = 3)
+
+module Swatch = struct
+  type t = { colour : Colour.t; label : string } [@@fieldglass generate]
+end
+
+let () =
+  let open Fieldglass in
+  let original = Swatch.{ colour = Colour.{ red = 3; green = 4; blue = 5 }; label = "grey" } in
+  let focus = compose Swatch._colour Colour._red in
+  assert (view focus original = 3);
+  let changed = set focus 8 original in
+  assert (view focus changed = 8 && Swatch.label changed = "grey");
+  assert (set focus (view focus original) original = original);
+  assert (set Box._contents "grey" Box.{ contents = 9 } = Box.{ contents = "grey" })