don't report vsnprintf(3) error as bug

strbuf_addf() has been reporting a negative return value of vsnprintf(3)
as a bug since f141bd8 (Handle broken vsnprintf implementations in
strbuf, 2007-11-13).  Other functions copied that behavior:

7b03c89 (add xsnprintf helper function, 2015-09-24)
5ef264d (strbuf.c: add `strbuf_insertf()` and `strbuf_vinsertf()`, 2019-02-25)
8d25663 (mem-pool: add mem_pool_strfmt(), 2024-02-25)

However, vsnprintf(3) can legitimately return a negative value if the
formatted output would be longer than INT_MAX.  Stop accusing it of
being broken and just report the fact that formatting failed.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

mem-pool.c

@@ -4,6 +4,7 @@
 
 #include "git-compat-util.h"
 #include "mem-pool.h"
+#include "gettext.h"
 
 #define BLOCK_GROWTH_SIZE (1024 * 1024 - sizeof(struct mp_block))
 
@@ -122,7 +123,7 @@ static char *mem_pool_strvfmt(struct mem_pool *pool, const char *fmt,
 	len = vsnprintf(next_free, available, fmt, cp);
 	va_end(cp);
 	if (len < 0)
-		BUG("your vsnprintf is broken (returned %d)", len);
+		die(_("unable to format message: %s"), fmt);
 
 	size = st_add(len, 1); /* 1 for NUL */
 	ret = mem_pool_alloc(pool, size);

strbuf.c

@@ -277,7 +277,7 @@ void strbuf_vinsertf(struct strbuf *sb, size_t pos, const char *fmt, va_list ap)
 	len = vsnprintf(sb->buf + sb->len, 0, fmt, cp);
 	va_end(cp);
 	if (len < 0)
-		BUG("your vsnprintf is broken (returned %d)", len);
+		die(_("unable to format message: %s"), fmt);
 	if (!len)
 		return; /* nothing to do */
 	if (unsigned_add_overflows(sb->len, len))
@@ -404,7 +404,7 @@ void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap)
 	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, cp);
 	va_end(cp);
 	if (len < 0)
-		BUG("your vsnprintf is broken (returned %d)", len);
+		die(_("unable to format message: %s"), fmt);
 	if (len > strbuf_avail(sb)) {
 		strbuf_grow(sb, len);
 		len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);

wrapper.c

@@ -670,7 +670,7 @@ int xsnprintf(char *dst, size_t max, const char *fmt, ...)
 	va_end(ap);
 
 	if (len < 0)
-		BUG("your snprintf is broken");
+		die(_("unable to format message: %s"), fmt);
 	if (len >= max)
 		BUG("attempt to snprintf into too-small buffer");
 	return len;