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 <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Makefile

@@ -342,6 +342,9 @@ all::
 # Define DEFAULT_HELP_FORMAT to "man", "info" or "html"
 # (defaults to "man") if you want to have a different default when
 # "git help" is called without a parameter specifying the format.
+#
+# Define GMTIME_UNRELIABLE_ERRORS if your gmtime() function does not
+# return NULL when it receives a bogus time_t.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1464,6 +1467,11 @@ ifneq (,$(XDL_FAST_HASH))
 	BASIC_CFLAGS += -DXDL_FAST_HASH
 endif
 
+ifdef GMTIME_UNRELIABLE_ERRORS
+	COMPAT_OBJS += compat/gmtime.o
+	BASIC_CFLAGS += -DGMTIME_UNRELIABLE_ERRORS
+endif
+
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK = NoThanks
 endif

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;
+}

config.mak.uname

@@ -189,6 +189,7 @@ ifeq ($(uname_S),FreeBSD)
 	endif
 	PYTHON_PATH = /usr/local/bin/python
 	HAVE_PATHS_H = YesPlease
+	GMTIME_UNRELIABLE_ERRORS = UnfortunatelyYes
 endif
 ifeq ($(uname_S),OpenBSD)
 	NO_STRCASESTR = YesPlease

git-compat-util.h

@@ -697,4 +697,11 @@ void warn_on_inaccessible(const char *path);
 /* Get the passwd entry for the UID of the current process. */
 struct passwd *xgetpwuid_self(void);
 
+#ifdef GMTIME_UNRELIABLE_ERRORS
+struct tm *git_gmtime(const time_t *);
+struct tm *git_gmtime_r(const time_t *, struct tm *);
+#define gmtime git_gmtime
+#define gmtime_r git_gmtime_r
+#endif
+
 #endif