printing of anonymous type parameters after strengthening

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13603 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

testsuite/tests/typing-gadts/test.ml

@@ -512,3 +512,9 @@ let f : type a. a ty -> a =
 let g : type a. a ty -> a =
   let () = () in
   fun x -> match x with Int y -> y;;
+
+(* Printing of anonymous variables *)
+
+module M = struct type _ t = int end;;
+module M = struct type _ t = T : int t end;;
+module N = M;;

testsuite/tests/typing-gadts/test.ml.principal.reference

@@ -309,4 +309,7 @@ Error: This expression has type < bar : int; foo : int; .. > as 'a
 #       type 'a ty = Int : int -> int ty
 #     val f : 'a ty -> 'a = <fun>
 #       val g : 'a ty -> 'a = <fun>
+#       module M : sig type _ t = int end
+# module M : sig type _ t = T : int t end
+# module N : sig type 'a t = 'a M.t = T : int t end
 # 

testsuite/tests/typing-gadts/test.ml.reference

@@ -295,4 +295,7 @@ Error: This expression has type < bar : int; foo : int; .. > as 'a
 #       type 'a ty = Int : int -> int ty
 #     val f : 'a ty -> 'a = <fun>
 #       val g : 'a ty -> 'a = <fun>
+#       module M : sig type _ t = int end
+# module M : sig type _ t = T : int t end
+# module N : sig type 'a t = 'a M.t = T : int t end
 # 

typing/printtyp.ml

@@ -683,6 +683,17 @@ let rec tree_of_type_decl id decl =
 
   let params = filter_params decl.type_params in
 
+  begin match decl.type_manifest with
+  | Some ty ->
+      let vars = free_variables ty in
+      List.iter
+        (function {desc = Tvar (Some "_")} as ty ->
+            if List.memq ty vars then ty.desc <- Tvar None
+          | _ -> ())
+        params
+  | None -> ()
+  end;
+
   List.iter add_alias params;
   List.iter mark_loops params;
   List.iter check_name_of_type (List.map proxy params);