Applying interface with type parameter on module without type parameter

[rand00]

Compiling the following with ocamlbuild bug.byte prints:

+ ocamlfind ocamlc -c -o bug.cmo bug.ml
Fatal error: exception Invalid_argument("List.iter2")
Command exited with code 2.
Compilation unsuccessful after building 2 targets (0 cached) in 00:00:00.

module type S = sig

  type 'a error = unit
  val get : unit -> _ error

end

module M : S = struct

  (* type 'a error = unit (\*< correct type*\)*)
  type error = unit
  let get () = failwith "not implemented"

end

.. and there is no error reported by Merlin in the code either

[Octachron]

This a 4.13 only bug (see #10836) that has been fixed in 4.14 (see #10952).

[Octachron]

I forgot on the spur of the moment: thanks for the report!