date: recognize bogus FreeBSD gmtime output

Most gmtime implementations return a NULL value when they
encounter an error (and this behavior is specified by ANSI C
and POSIX).  FreeBSD's implementation, however, will simply
leave the "struct tm" untouched.  Let's also recognize this
and convert it to a NULL (with this patch, t4212 should pass
on FreeBSD).

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

1 files changed, 29 insertions, 0 deletions

diff --git a/compat/gmtime.c b/compat/gmtime.c
new file mode 100644
index 0000000000..e8362dd2b9
--- /dev/null
+++ b/compat/gmtime.c
@@ -0,0 +1,29 @@
+#include "../git-compat-util.h"
+#undef gmtime
+#undef gmtime_r
+
+struct tm *git_gmtime(const time_t *timep)
+{
+	static struct tm result;
+	return git_gmtime_r(timep, &result);
+}
+
+struct tm *git_gmtime_r(const time_t *timep, struct tm *result)
+{
+	struct tm *ret;
+
+	memset(result, 0, sizeof(*result));
+	ret = gmtime_r(timep, result);
+
+	/*
+	 * Rather than NULL, FreeBSD gmtime simply leaves the "struct tm"
+	 * untouched when it encounters overflow. Since "mday" cannot otherwise
+	 * be zero, we can test this very quickly.
+	 */
+	if (ret && !ret->tm_mday) {
+		ret = NULL;
+		errno = EOVERFLOW;
+	}
+
+	return ret;
+}