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

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

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 107377 has been marked as a duplicate of this bug. ***

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

[mpolacek at gcc dot gnu.org]

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

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
FWIW, Clang implements this warning:

$ xclang++ -c -xc j.c -Wduplicate-enum
j.c:1:33: warning: element 'foo' has been implicitly assigned 0 which another
element has been assigned [-Wduplicate-enum]
enum status { ok = 0, err = -1, foo, bar };
                                ^~~
j.c:1:15: note: element 'ok' also has value 0
enum status { ok = 0, err = -1, foo, bar };
              ^~~~~~

I suppose we could do a binary search when adding a new enumerator in
build_enumerator, see if an enumerator with the same value is already present,
and warn if so.

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

[marxin at gcc dot gnu.org]

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

--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #3)
> FWIW, Clang implements this warning:

Oh, I was unable to find the option (only tried -Werror and -Wextra).

@Marek: please add it!

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

[mpolacek at gcc dot gnu.org]

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

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #4)
> @Marek: please add it!

Anything to oblige ye, my fellow.

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

[marxin at gcc dot gnu.org]

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

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=107386

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #5)
> (In reply to Martin Liška from comment #4)
> > @Marek: please add it!
> 
> Anything to oblige ye, my fellow.

It would pay off my friend (PR107386).

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

[trashyankes at wp dot pl]

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

trashyankes at wp dot pl changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |trashyankes at wp dot pl

--- Comment #7 from trashyankes at wp dot pl ---
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,
};

```

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

[jakub at gcc dot gnu.org]

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

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 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...

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

[austern at apple dot com]

Consider the following enumeration declaration:
  enum status { ok = 0, err = -1, foo, bar };
The enumerators 'ok' and 'foo' will have the same value.  This may be what the programmer intended, 
but it's more likely to be an oversight.  The C and C++ front ends should have a warning (which 
probably should not be enabled by default or with -Wall) for enumerations whose enumerators have 
duplicate values, since duplicates are likely to be a sign of programmer error.

-- 
           Summary: gcc should have an option to warn about enumerations
                    with duplicate values
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: austern at apple dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: all
  GCC host triplet: all
GCC target triplet: all


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

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

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-29 02:47 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2004-06-29 02:47:43
               date|                            |


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