working from the current git head of gpgme (4746c5c9e2dd9a3ee471a429c19bc1f7fd1d07db), i see many warnings from debug.h, when using gcc (Debian 8.3.0-6) 8.3.0. One small example:
In file included from data-compat.c:36:
debug.h: In function '_trace_err':
debug.h:138:45: warning: zero-length gnu_printf format string [-Wformat-zero-length]
_gpgme_debug (lvl, 3, func, NULL, NULL, "");
^~
In file included from signers.c:34:
debug.h: In function '_trace_err':
debug.h:138:45: warning: zero-length gnu_printf format string [-Wformat-zero-length]
_gpgme_debug (lvl, 3, func, NULL, NULL, "");
^~
signers.c: In function 'gpgme_signers_clear':
signers.c:59:49: warning: zero-length gnu_printf format string [-Wformat-zero-length]
TRACE (DEBUG_CTX, "gpgme_signers_clear", ctx, "");
^~
debug.h:126:19: note: in definition of macro 'TRACE'
__VA_ARGS__); \
^~~~~~~~~~~
signers.c: In function 'gpgme_signers_add':
signers.c:92:14: warning: zero-length gnu_printf format string [-Wformat-zero-length]
TRACE_SUC ("");
^~
debug.h:181:19: note: in definition of macro 'TRACE_SUC'
__VA_ARGS__); \
^~~~~~~~~~~they seem to have been introduced between 1.12 and 1.13 (probably in 5857491a2aa7d4975100d90f1ad62c08aa345e3e).
Please clean these up! they make it hard to see whether there are any real warnings we should be concerned about.