Original bug ID: 4487
Reporter: jm
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2012-03-24T14:01:41Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.10+dev
Fixed in version: 3.12.1+dev
Category: ~DO NOT USE (was: OCaml general)
Duplicate of: #5164
Related to: #5037 #5061
Monitored by: "Julien Signoles"

Bug description

% ocamlc -v
The Objective Caml compiler, version 3.10.2+dev2 (2008-01-22)
Standard library directory: /usr/local/lib/ocaml

In a module where two values have the same name and type,
ocamlc does not complain if the related signature has two entries:

% cat m.ml
module M
: sig val x : int
val x : int end
= struct let x = 0
let x = 42 end;;
print_endline (string_of_int M.x)

% ocamlc -i m.ml
module M : sig val x : int end
% ocamlc -c m.ml
% ocaml m.ml
42

But if the signature is inside a module type,
ocamlc does complain:

% cat t.ml
module type T
= sig val x : int
val x : int end
module M
: T
= struct let x = 0
let x = 42 end;;
print_endline (string_of_int M.x)

% ocamlc -i t.ml
module type T = sig val x : int val x : int end
module M : T
% ocamlc -c t.ml
The implementation t.ml does not match the interface (inferred signature):
Module type declarations do not match:
module type T = sig val x : int val x : int end
does not match
module type T = sig val x : int val x : int end
Illegal permutation of structure fields
2% ocaml t.ml
42

I would have expected ocamlc to accept a redundant value in a module type,
as ocaml does. Also, note that I'm not posting this report for the sake of hair splitting, but in order to bring into awareness a real-life issue I've encountered while dealing with module type inclusions.

Thanks for considering.

Additional information

Currently I'm somehow avoiding my real-life problem with Piotr Wieczorek's sigops.patch at:
http://rainbow.mimuw.edu.pl/~pw189451/ocaml/