[Bug c/80619] New: bad fix-it hint for GCC %lu directive with int argument: %wu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80619

            Bug ID: 80619
           Summary: bad fix-it hint for GCC %lu directive with int
                    argument: %wu
           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: ---

When the %lu printf directive in a function decorated with attribute format
__gcc_diag__ is passed an int argument GCC issues a warning as expected, but
then proceeds to suggest to replace the directive with %wu.  This suggestion is
wrong because %wu expects an unsigned HOST_WIDE_INT argument, a type that is
typically wider than int.  The correct hint is "%u".

$ cat x.c && gcc -O2 -S -Wall -Wpedantic x.c
void f (const char*, ...) __attribute__ ((format (__gcc_diag__, 1, 2)));

void h (void)
{
  f ("%lu", 0);
}
x.c: In function ‘h’:
x.c:5:9: warning: format ‘%lu’ expects argument of type ‘long unsigned int’,
but argument 2 has type ‘int’ [-Wformat=]
   f ("%lu", 0);
       ~~^
       %wu