Comment author: @gasche

Reproduced under 4.06.0.

Comment author: Iguernlala

I forgot to say that trying to disable this warning with an annotation [@@@ocaml.warning "-60"] did not work

[Edited]
Actually, I manage to disable the warning if I put the annotation before 'module rec M ...'. (I had tried to put the annotation before 'and module X1 ...' previously)

Comment author: @mshinwell

Here is another, probably related, example which I came across this week.

w60.ml

module type S = sig val f : unit -> unit end

module F (X : S) = struct let f () = X.f () end

module rec A : S =
F (struct let f () = B.f () end)
and B : S =
F (struct let f () = failwith "ok" end)

let f = A.f

let () = f ()

w60.mli

val f : unit -> unit

Using a recent trunk:

$ ocamlc w60.mli
$ ocamlc -w +60 -o w60 w60.ml
File "w60.ml", line 7, characters 0-42:
Warning 60: unused module B.
$ ./w60
Fatal error: exception Failure("ok")

The warning is bogus, as evidenced by the exception, which shows that [B] was used.

The bogus warning does not appear if the .mli file is absent.

Comment author: @mshinwell

As an aside: the following version produces a runtime exception:

Fatal error: exception Undefined_recursive_module("w60.ml", 23, 2)

This surprised me at first, but it appears to be related to Mantis 2629. It would indeed be nice if there were a compile-time check for this as suggested in that issue:

module type S = sig val f : unit -> unit end

module F (X : S) = struct let f = X.f end

module rec A : S =
F (struct let f = B.f end)
and B : S =
F (struct let f () = failwith "ok" end)

let f = A.f

let () = f ()

Duplicate of #7522 ?

This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc.

This was fixed by #9393