Add more new test cases for module inclusion errors

These test cases will also have improved error messages in the next
non-test commit.  They come from the work done to address reviewer
comments for ocaml#10407.

testsuite/tests/typing-gadts/return_type.ml

@@ -0,0 +1,36 @@
+(* TEST
+   * expect
+*)
+
+type i = int
+
+type 'a t = T : i
+[%%expect{|
+type i = int
+Line 3, characters 16-17:
+3 | type 'a t = T : i
+                    ^
+Error: Constraints are not satisfied in this type.
+       Type i should be an instance of 'a t
+|}]
+
+type 'a t = T : i t
+type 'a s = 'a t = T : i t
+[%%expect{|
+type 'a t = T : i t
+Line 2, characters 23-26:
+2 | type 'a s = 'a t = T : i t
+                           ^^^
+Error: Constraints are not satisfied in this type.
+       Type i t should be an instance of 'a s
+|}]
+
+type 'a t = T : i s
+and  'a s = 'a t
+[%%expect{|
+Line 1, characters 16-19:
+1 | type 'a t = T : i s
+                    ^^^
+Error: Constraints are not satisfied in this type.
+       Type i s should be an instance of 'a t
+|}]

testsuite/tests/typing-modules/extension_constructors_errors_test.ml

@@ -42,3 +42,20 @@ Error: Signature mismatch:
          type t += A
        A private type would be revealed.
 |}];;
+
+module M2 : sig type t += A end = struct type t += private A | B end;;
+[%%expect{|
+Line 1, characters 34-68:
+1 | module M2 : sig type t += A end = struct type t += private A | B end;;
+                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t += private A | B  end
+       is not included in
+         sig type t += A end
+       Extension declarations do not match:
+         type t += private A
+       is not included in
+         type t += A
+       A private type would be revealed.
+|}];;

testsuite/tests/typing-modules/inclusion_errors.ml

@@ -538,6 +538,27 @@ Error: Signature mismatch:
          val f : s -> s
 |}];;
 
+module M : sig
+  val f : 'a -> float
+end = struct
+  let f : 'b -> int = fun _ -> 0
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   let f : 'b -> int = fun _ -> 0
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig val f : 'b -> int end
+       is not included in
+         sig val f : 'a -> float end
+       Values do not match:
+         val f : 'b -> int
+       is not included in
+         val f : 'a -> float
+|}]
+
 module M : sig
   val x : 'a list ref
 end = struct
@@ -1236,3 +1257,311 @@ Error: Signature mismatch:
        is not included in
          type t = private float
 |}];;
+
+module M : sig
+  type t = A
+end = struct
+  type t = private A
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A end
+       is not included in
+         sig type t = A end
+       Type declarations do not match:
+         type t = private A
+       is not included in
+         type t = A
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = A | B
+end = struct
+  type t = private A | B
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A | B
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A | B end
+       is not included in
+         sig type t = A | B end
+       Type declarations do not match:
+         type t = private A | B
+       is not included in
+         type t = A | B
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = A of { x : int; y : bool }
+end = struct
+  type t = private A of { x : int; y : bool }
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A of { x : int; y : bool }
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A of { x : int; y : bool; } end
+       is not included in
+         sig type t = A of { x : int; y : bool; } end
+       Type declarations do not match:
+         type t = private A of { x : int; y : bool; }
+       is not included in
+         type t = A of { x : int; y : bool; }
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = { x : int; y : bool }
+end = struct
+  type t = private { x : int; y : bool }
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private { x : int; y : bool }
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private { x : int; y : bool; } end
+       is not included in
+         sig type t = { x : int; y : bool; } end
+       Type declarations do not match:
+         type t = private { x : int; y : bool; }
+       is not included in
+         type t = { x : int; y : bool; }
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = A
+end = struct
+  type t = private A | B
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A | B
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A | B end
+       is not included in
+         sig type t = A end
+       Type declarations do not match:
+         type t = private A | B
+       is not included in
+         type t = A
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = A | B
+end = struct
+  type t = private A
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A end
+       is not included in
+         sig type t = A | B end
+       Type declarations do not match:
+         type t = private A
+       is not included in
+         type t = A | B
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = { x : int }
+end = struct
+  type t = private { x : int; y : bool }
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private { x : int; y : bool }
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private { x : int; y : bool; } end
+       is not included in
+         sig type t = { x : int; } end
+       Type declarations do not match:
+         type t = private { x : int; y : bool; }
+       is not included in
+         type t = { x : int; }
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = { x : int; y : bool }
+end = struct
+  type t = private { x : int }
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private { x : int }
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private { x : int; } end
+       is not included in
+         sig type t = { x : int; y : bool; } end
+       Type declarations do not match:
+         type t = private { x : int; }
+       is not included in
+         type t = { x : int; y : bool; }
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = A | B
+end = struct
+  type t = private { x : int; y : bool }
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private { x : int; y : bool }
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private { x : int; y : bool; } end
+       is not included in
+         sig type t = A | B end
+       Type declarations do not match:
+         type t = private { x : int; y : bool; }
+       is not included in
+         type t = A | B
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = { x : int; y : bool }
+end = struct
+  type t = private A | B
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private A | B
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private A | B end
+       is not included in
+         sig type t = { x : int; y : bool; } end
+       Type declarations do not match:
+         type t = private A | B
+       is not included in
+         type t = { x : int; y : bool; }
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = [`A]
+end = struct
+  type t = private [> `A | `B]
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private [> `A | `B]
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private [> `A | `B ] end
+       is not included in
+         sig type t = [ `A ] end
+       Type declarations do not match:
+         type t = private [> `A | `B ]
+       is not included in
+         type t = [ `A ]
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = [`A]
+end = struct
+  type t = private [< `A | `B]
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private [< `A | `B]
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private [< `A | `B ] end
+       is not included in
+         sig type t = [ `A ] end
+       Type declarations do not match:
+         type t = private [< `A | `B ]
+       is not included in
+         type t = [ `A ]
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = [`A]
+end = struct
+  type t = private [< `A | `B > `A]
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private [< `A | `B > `A]
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private [< `A | `B > `A ] end
+       is not included in
+         sig type t = [ `A ] end
+       Type declarations do not match:
+         type t = private [< `A | `B > `A ]
+       is not included in
+         type t = [ `A ]
+       A private type would be revealed.
+|}];;
+
+module M : sig
+  type t = < m : int >
+end = struct
+  type t = private < m : int; .. >
+end;;
+[%%expect{|
+Lines 3-5, characters 6-3:
+3 | ......struct
+4 |   type t = private < m : int; .. >
+5 | end..
+Error: Signature mismatch:
+       Modules do not match:
+         sig type t = private < m : int; .. > end
+       is not included in
+         sig type t = < m : int > end
+       Type declarations do not match:
+         type t = private < m : int; .. >
+       is not included in
+         type t = < m : int >
+       A private type would be revealed.
+|}];;