[Bug c/80398] New: missing -Wattributes on a misplaced attribute packed in an enum definition

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80398

            Bug ID: 80398
           Summary: missing -Wattributes on a misplaced attribute packed
                    in an enum definition
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC (in C mode) fails to diagnose the following declaration with the misplaced
packed attribute in the test case below.  G++ issues the expected warning.

  __attribute__ ((packed)) enum E0 { e0 };   // attribute ignored, missing
warning

$ (set -x && cat a.c && for lang in c c++; do gcc -S -Wall -Wextra -Wpedantic
-Wattributes -Wignored-attributes -x$lang a.c; done)
+ cat a.c
__attribute__ ((packed)) enum E0 { e0 };
enum __attribute__ ((packed)) E1 { e1 }; 
enum E2 { e2 } __attribute__ ((packed));

#if __cplusplus
#  define A(e) static_assert (e, #e)
#else
#  define A(e) _Static_assert (e, #e)
#endif

A (sizeof (enum E0) == 1);
A (sizeof (enum E1) == 1);
A (sizeof (enum E2) == 1);
+ for lang in c c++
+ gcc -S -Wall -Wextra -Wpedantic -Wattributes -Wignored-attributes -xc a.c
a.c:8:16: error: static assertion failed: "sizeof (enum E0) == 1"
 #  define A(e) _Static_assert (e, #e)
                ^
a.c:11:1: note: in expansion of macro ‘A’
 A (sizeof (enum E0) == 1);
 ^
+ for lang in c c++
+ gcc -S -Wall -Wextra -Wpedantic -Wattributes -Wignored-attributes -xc++ a.c
a.c:1:31: warning: attribute ignored in declaration of ‘enum E0’ [-Wattributes]
 __attribute__ ((packed)) enum E0 { e0 };
                               ^~
a.c:1:31: note: attribute for ‘enum E0’ must follow the ‘enum’ keyword
a.c:6:16: error: static assertion failed: sizeof (enum E0) == 1
 #  define A(e) static_assert (e, #e)
                ^
a.c:11:1: note: in expansion of macro ‘A’
 A (sizeof (enum E0) == 1);
 ^