Remove extra module from Vfile_kind functor

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/super_context.ml

@@ -534,10 +534,10 @@ end
 module Pkg_version = struct
   open Build.O
 
-  module V = Vfile_kind.Make(struct type t = string option end)
-      (struct
-        let t = Sexp.To_sexp.(option string)
-      end)
+  module V = Vfile_kind.Make(struct
+      type t = string option
+      let t = Sexp.To_sexp.(option string)
+    end)
 
   let spec sctx (p : Package.t) =
     let fn =

src/vfile_kind.ml

@@ -43,14 +43,16 @@ let eq (type a) (type b)
   Id.eq A.id B.id
 
 module Make
-    (T : sig type t end)
-    (To_sexp : sig val t : T.t Sexp.To_sexp.t end)
+    (T : sig
+       type t
+       val t : t Sexp.To_sexp.t
+     end)
   : S with type t = T.t =
 struct
   type t = T.t
 
   (* XXX dune dump should make use of this *)
-  let _t = To_sexp.t
+  let _t = T.t
 
   module P = Utils.Persistent(struct
       type nonrec t = t

src/vfile_kind.mli

@@ -20,6 +20,8 @@ type 'a t = (module S with type t = 'a)
 val eq : 'a t -> 'b t -> ('a, 'b) eq option
 
 module Make
-    (T : sig type t end)
-    (To_sexp : sig val t : T.t Sexp.To_sexp.t end)
+    (T : sig
+       type t
+       val t : t Sexp.To_sexp.t
+     end)
   : S with type t = T.t