ocaml#9385 from lpw25/fix-copy-scope-bugs

Fix incorrect copy_scopes in Subst

(cherry picked from commit 288bb81)
(cherry picked from commit 2e08e99)

testsuite/tests/typing-modules/pr9384.ml

@@ -0,0 +1,39 @@
+(* TEST
+   * expect
+*)
+
+module M : sig
+  type 'a t := [< `A ] as 'a
+  val f : 'a -> 'a t
+end = struct
+  let f x = x
+end;;
+[%%expect{|
+module M : sig val f : ([< `A ] as 'a) -> 'a end
+|}]
+
+type foo = { foo : 'a. ([< `A] as 'a) -> 'a }
+
+module Foo (X : sig type 'a t := [< `A ] as 'a type foo2 = foo = { foo : 'a. 'a t -> 'a t } end) = struct
+    let f { X.foo } = foo
+end;;
+[%%expect{|
+type foo = { foo : 'a. ([< `A ] as 'a) -> 'a; }
+module Foo :
+  functor
+    (X : sig type foo2 = foo = { foo : 'a. ([< `A ] as 'a) -> 'a; } end) ->
+    sig val f : X.foo2 -> ([< `A ] as 'a) -> 'a end
+|}]
+
+type bar = { bar : 'a. ([< `A] as 'a) -> 'a }
+
+module Bar (X : sig type 'a t := 'a type bar2 = bar = { bar : 'a. ([< `A] as 'a) t -> 'a t } end) = struct
+  let f { X.bar } = bar
+end;;
+[%%expect{|
+type bar = { bar : 'a. ([< `A ] as 'a) -> 'a; }
+module Bar :
+  functor
+    (X : sig type bar2 = bar = { bar : 'a. ([< `A ] as 'a) -> 'a; } end) ->
+    sig val f : X.bar2 -> ([< `A ] as 'a) -> 'a end
+|}]

typing/subst.ml

@@ -497,8 +497,8 @@ and signature_item' copy_scope scoping s comp =
   | Sig_class_type(id, d, rs, vis) ->
       Sig_class_type(id, cltype_declaration' copy_scope s d, rs, vis)
 
-and signature_item s comp =
-  For_copy.with_scope (fun copy_scope -> signature_item' copy_scope s comp)
+and signature_item scoping s comp =
+  For_copy.with_scope (fun copy_scope -> signature_item' copy_scope scoping s comp)
 
 and module_declaration scoping s decl =
   {
@@ -527,9 +527,10 @@ let merge_path_maps f m1 m2 =
 let type_replacement s = function
   | Path p -> Path (type_path s p)
   | Type_function { params; body } ->
-     let params = List.map (type_expr s) params in
-     let body = type_expr s body in
-     Type_function { params; body }
+    For_copy.with_scope (fun copy_scope ->
+     let params = List.map (typexp copy_scope s) params in
+     let body = typexp copy_scope s body in
+     Type_function { params; body })
 
 (* Composition of substitutions:
      apply (compose s1 s2) x = apply s2 (apply s1 x) *)