[Bug middle-end/111775] New: -Wstrict-flex-arrays missing diagnostics with unions

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111775

            Bug ID: 111775
           Summary: -Wstrict-flex-arrays missing diagnostics with unions
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crrodriguez at opensuse dot org
  Target Milestone: ---

following code is not diagnosed

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

struct foo {
        int dum;
union {
/* or  [1] */
        char a[0];
        wchar_t b[0];
      } fn;
};


int main(void)
{
        struct foo *f = malloc(sizeof(*f));
       /* or really any use of the union does not matter */
        printf("%p", f->fn.b);
        free(f);
        return 0;

}

compile options

-Wall -fstrict-flex-arrays -Werror=strict-flex-arrays -O2

This test is a silly mockup of real widespread code, which goes undiagnosed
until test suites run and/or is built with ubsan.