Warning message for unused exception uses "extension", which is confusing.

[vicuna]

Original bug ID: 7139
Reporter: @gasche
Assigned to: @mshinwell
Status: resolved (set by @mshinwell on 2016-12-12T15:19:50Z)
Resolution: fixed
Priority: normal
Severity: text
Target version: 4.03.1+dev
Fixed in version: 4.04.0
Category: ~DO NOT USE (was: OCaml general)
Monitored by: @diml @hcarty

Bug description

Having the unused exception
exception Bad_magic_version of version

gives the following error message
File "utils/misc.ml", line 660, characters 2-40:
Warning 38: unused extension constructor Bad_magic_version.

I think that this is confusing for people that don't know about "extension constructor", and do not need to know about it. The error message should say

Warning 38: unused exception Bad_magic_version.

Steps to reproduce

$ cat test.ml
module M : sig end = struct
exception Foo of int
end

$ ocamlc -w +38 -c test.ml
File "test.ml", line 2, characters 2-22:
Warning 38: unused extension constructor Foo.

[vicuna]

Comment author: @gasche

I'm pushing back to 4.04; this usability issue is already present in 4.02.3, so it can wait for 4.04.

I proposed a patch at

#552

[vicuna]

Comment author: @mshinwell

#552 has now been merged.