(* TEST
 flags = " -short-paths ";
 expect;
*)

module M = struct type t = T end

type t = M.t

let x : M.t = S
[%%expect {|
module M : sig type t = T end
type t = M.t
Line 5, characters 14-15:
5 | let x : M.t = S
                  ^
Error: This variant expression is expected to have type "t"
       There is no constructor "S" within type "t"
|}]

module M = struct
  class c = object method foo = 3 end
end

type c = M.c

let () = (new M.c)#bar
[%%expect {|
module M : sig class c : object method foo : int end end
type c = M.c
Line 7, characters 9-18:
7 | let () = (new M.c)#bar
             ^^^^^^^^^
Error: This expression has type "c"
       It has no method "bar"
|}]


(** Known issue: how to print existential types with equality in scope? *)

type _ ty = Char : char ty
type pair = Pair : 'a ty * 'a -> pair

(* In the following function, we would like to see that [x] has type [char],
   rather than an existential type *)
let f = function
  | Pair (Char, x) -> x + 1
[%%expect {|
type _ ty = Char : char ty
type pair = Pair : 'a ty * 'a -> pair
Line 9, characters 22-23:
9 |   | Pair (Char, x) -> x + 1
                          ^
Error: The value "x" has type "$a" but an expression was expected of type "int"
       Hint: "$a" is an existential type bound by the constructor "Pair".
|}]

type _ ty = Char : char ty
type pair = Pair : 'a ty * 'a -> pair

(* In the following function, an error report with the existential type is more
   useful than one stating that type [char] would escape the scope *)
let f = function
  | Pair (Char, x) -> if true then x else 'd'
[%%expect {|
type _ ty = Char : char ty
type pair = Pair : 'a ty * 'a -> pair
Line 7, characters 35-36:
7 |   | Pair (Char, x) -> if true then x else 'd'
                                       ^
Error: The value "x" has type "$a" but an expression was expected of type "'a"
       This instance of "$a" is ambiguous:
       it would escape the scope of its equation
       Hint: "$a" is an existential type bound by the constructor "Pair".
|}]

(** Cycle type definitions *)

type 'a t = 'a t
[%%expect {|
Line 3, characters 0-16:
3 | type 'a t = 'a t
    ^^^^^^^^^^^^^^^^
Error: The type abbreviation "t" is cyclic:
         "'a t" = "'a t"
|}]

type 'a t = 'a u
and 'a u = 'a v * 'a
and 'a v = 'a w list
and 'a w = 'a option z
and 'a z = 'a t
[%%expect {|
Line 1, characters 0-16:
1 | type 'a t = 'a u
    ^^^^^^^^^^^^^^^^
Error: The type abbreviation "t" is cyclic:
         "'a t" = "'a u",
         "'a u" = "'a v * 'a",
         "'a v * 'a" contains "'a v",
         "'a v" = "'a w list",
         "'a w list" contains "'a w",
         "'a w" = "'a option z",
         "'a option z" = "'a option t"
|}]


type 'a u = < x : 'a>
and 'a t = 'a t u;;
[%%expect{|
Line 2, characters 0-17:
2 | and 'a t = 'a t u;;
    ^^^^^^^^^^^^^^^^^
Error: The type abbreviation "t" is cyclic:
         "'a t u" contains "'a t",
         "'a t" = "'a t u",
         "'a t u" contains "'a t"
|}];; (* fails since 4.04 *)


module rec A : sig type t = B.t -> int end = struct type t = B.t -> int end
       and B : sig type t = A.t end = struct type t = A.t end;;
[%%expect {|
Line 1, characters 0-75:
1 | module rec A : sig type t = B.t -> int end = struct type t = B.t -> int end
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: The definition of "A.t" contains a cycle:
         "B.t -> int" contains "B.t",
         "B.t" = "B.t",
         "B.t" = "B.t -> int",
         "B.t -> int" contains "B.t",
         "B.t" = "B.t"
|}]