[Bug c/115109] New: Incorrect type of enumeration constant in redeclaration of enumeration constant (C23)

["luigighiron at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115109

            Bug ID: 115109
           Summary: Incorrect type of enumeration constant in
                    redeclaration of enumeration constant (C23)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: luigighiron at gmail dot com
  Target Milestone: ---

GCC does not accept the following code:

static_assert(INT_WIDTH<42&&LONG_WIDTH>=42);
enum E{a=1UL<<40,b=1};
enum E{a=1ULL<<40,b=_Generic(a,unsigned long:1,default:2)};

The static_assert is there to document the assumptions that should make this
code valid. Here is the relevant part of the standard:

> During the processing of each enumeration constant in the enumerator list,
> the type of the enumeration constant shall be:
> 
> - the previously declared type, if it is a redeclaration of the same
>   enumeration constant; or,
> 
> - the enumerated type, for an enumeration with fixed underlying type; or,
> 
> - int, if there are no previous enumeration constants in the enumerator list
>   and no explicit = with a defining integer constant expression; or,
> 
> - int, if given explicitly with = and the value of the integer constant
>   expression is representable by an int; or,
> 
> - the type of the integer constant expression, if given explicitly with = and
>   if the value of the integer constant expression is not representable by int;
>   or,
> 
>   ...
Section 6.7.3.3 "Enumeration specifiers" Paragraph 12 N3220

The types of the enumeration constants 'a' and 'b' in the first enumeration
specifier should be unsigned long and int, respectively. Then in the second
enumeration declaration, they should have the same types as the first
enumeration declaration because of the first item in the list in the above
quote. GCC does not seem to follow this and makes the type of the enumeration
constant 'a' unsigned long long because the type of the expression is unsigned
long long.