[Bug c/16186] gcc should have an option to warn about enumerations with duplicate values

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=16186

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to trashyankes from comment #7)
> Should be way to disable/enable this warning per `enum`?
> Like:
> 
> ```
> enum [[gnu::enum_unique]] X
> {
>   I = 1,
>   J = 2,
> };
> 
> enum [[gnu::enum_not_unique]] Y
> {
>   K = 1,
>   L = 1,
> };
> 
> ```

No, it should warn solely if enumerator gets implicitly assigned value of some
other enumerator.  After all, the clang wording also mentions that:
element 'D' has been implicitly assigned 5 which another element has been
assigned [-Wduplicate-enum]
If there is = value for it, we should never warn, that is most likely
completely intentional.
Of course, we should use better wording, because we should talk about
enumerators, not elements...