Fix PR#7321

Changes

@@ -83,6 +83,10 @@ Working version
 - PR#7261: Warn on type constraints in GADT declarations
   (Jacques Garrigue, report by Fabrice Le Botlan)
 
+- PR#7321: Private type in signature clashes with type definition via
+  functor instantiation
+  (Jacques Garrigue, report by Markus Mottl)
+
 - PR#7344: Inconsistent behavior with type annotations on let
   (Jacques Garrigue, report by Leo White)
 

testsuite/tests/typing-modules-bugs/pr7321_ok.ml

@@ -0,0 +1,8 @@
+module type S = sig type 'a t end
+module type Sp = sig type 'a t = private 'a array end
+
+module Id (S : S) = S
+
+module M : Sp = struct
+  include Id (struct type 'a t = 'a array end)
+end

typing/includecore.ml

@@ -288,6 +288,9 @@ let type_declarations ?(equality = false) env name decl1 id decl2 =
     else []
   in
   if err <> [] then err else
+  let need_variance =
+    abstr || decl1.type_private = Private || decl1.type_kind = Type_open in
+  if not need_variance then [] else
   let abstr = abstr || decl2.type_private = Private in
   let opn = decl2.type_kind = Type_open && decl2.type_manifest = None in
   let constrained ty = not (Btype.(is_Tvar (repr ty))) in