[Bug c/47901] New: -Wall should not imply -Wformat-zero-length by default

["anders at kaseorg dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47901

           Summary: -Wall should not imply -Wformat-zero-length by default
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: anders@kaseorg.com


There is nothing wrong with printf("") or custom_printf_like_function(foo, "").
 There are plenty of reasons to write such code: for example, when using a
macro that sometimes expands to the empty string, or if
custom_printf_like_function does something else with foo in addition to using
the format string, or if the string is used for something other than printing
and you really just want the empty string there.

gcc/c-format.c contains a comment that says “If the format is an empty string,
this should be counted similarly to the case of extra format arguments.”  But
those are not actually similar.  Extra format arguments clearly indicate that
the code was not written as intended, because the extra arguments could be
removed with no effects; but a zero-length string is there for a reason and
can’t just be removed.

When GCC complains about legitimate empty format strings as soon as -Wall is
turned on, it only leads to frustration with -Wall.  This leads some users to
give up on -Wall altogether, and thus to miss many of the real problems -Wall
would find; and leads others to come up with brain-damaged workarounds like
adding a useless space:
http://git.kernel.org/linus/6f131ce1dfa9b283ddc212df42b015d152c670a5

Can we change -Wformat-zero-length to default to off unless explicitly
requested?

See also:
http://gcc.gnu.org/ml/gcc-patches/2002-05/msg01469.html
http://ewx.livejournal.com/517490.html
http://www.mail-archive.com/qemu-devel@nongnu.org/msg43910.html