parse-options API: add a usage_msg_optf()

Add a usage_msg_optf() as a shorthand for the sort of
usage_msg_opt(xstrfmt(...)) used in builtin/stash.c. I'll make more
use of this function in builtin/cat-file.c shortly.

The disconnect between the "..." and "fmt" is a bit unusual, but it
works just fine and this keeps it consistent with usage_msg_opt(),
i.e. a caller of it can be moved to usage_msg_optf() and not have to
have its arguments re-arranged.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/parse-options.c b/parse-options.c
index fc5b43ff0b..5a319dda7d 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -1078,3 +1078,16 @@ void NORETURN usage_msg_opt(const char *msg,
 	fprintf(stderr, "fatal: %s\n\n", msg);
 	usage_with_options(usagestr, options);
 }
+
+void NORETURN usage_msg_optf(const char * const fmt,
+			     const char * const *usagestr,
+			     const struct option *options, ...)
+{
+	struct strbuf msg = STRBUF_INIT;
+	va_list ap;
+	va_start(ap, options);
+	strbuf_vaddf(&msg, fmt, ap);
+	va_end(ap);
+
+	usage_msg_opt(msg.buf, usagestr, options);
+}