This is a wrapper around __attribute__ ((__nonstring__)). Traditionally
this was used to mark char array variables that intentionally lacked a
terminating NUL byte, this would then cause warning to either be quelled
or emitted for various memory/string functions.

GCC 15 introduced a new warning, Wunterminated-string-initialization,
which will always warn on things like

  static const char hex[16] = "0123456789ABCDEF";

However this is very much intentionally not NUL terminated.

When the Wunterminated-string-initialization patch went in, the
"nonstriong" attribute didn't quell this warning, however a patch has
since gone in (prior to the GCC 15 release) to enable this attribute to
quell this warning.

In Unit we disabled this new warning with an eye to being able to
re-enable it again, this patch is the first in a series to do just that.

So the above example would become

  static const char hex[16] NXT_NONSTRING = "0123456789ABCDEF";

Link: <https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=44c9403ed1833ae71a59e84f9e37af3182be0df5>
Link: <https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=622968990beee7499e951590258363545b4a3b57>
Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178#c21>
Cc: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Future releases of GCC are planning to remove[0] default support for
some old features that were removed from C99 but GCC still accepts.

We can test for these changes by using the following -Werror=
directives

  -Werror=implicit-int
  -Werror=implicit-function-declaration
  -Werror=int-conversion
  -Werror=strict-prototypes
  -Werror=old-style-definition

Doing so revealed an issue with the auto/ tests in that the test
programs always define main as

  int main()

rather than

  int main(void)

which results in a bunch of errors like

build/autotest.c:3:23: error: function declaration isn't a prototype [-Werror=strict-prototypes]
    3 |                   int main() {
      |                       ^~~~
build/autotest.c: In function 'main':
build/autotest.c:3:23: error: old-style function definition [-Werror=old-style-definition]

The fix was easy, it only required fixing the main prototype with

  find -type f -exec sed -i 's/int main() {/int main(void) {/g' {} \;

Regardless of these upcoming GCC changes, this is probably a good thing
to do anyway for correctness.

[0]: https://fedoraproject.org/wiki/Changes/PortingToModernC

Link: <https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/CJXKTLXJUPZ4F2C2VQOTNMEA5JAUPMBD/>
Link: <https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/6SGHPHPAXKCVJ6PUZ57WVDQ5TDBVIRMF/>
Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

When testing some configurations of compilers and OSes, I noticed
that clang(1) 13 on Debian caused a function to be compiled but
unused, and the compiler triggered a compile error.

To avoid that error, use __attribute__((__unused__)).  Let's call
our wrapper NXT_MAYBE_UNUSED, since it describes itself more
precisely than the GCC attribute name.  It's also the name that
C2x (likely C23) has given to the standard attribute, which is
[[maybe_unused]], so it's also likely to be more readable because
of that name being in ISO C.

Thanks to 洪志道 (Hong Zhi Dao).