nstrftime: be more predictable about errno

This aligns nstrftime better with draft POSIX 202x strftime.
* lib/nstrftime.c: Include errno.h.
(width_add, __strftime_internal): Set errno on failure,
and preserve it on success.  Check for mktime_z failure.
* modules/nstrftime (Depends-on): Add errno.
* modules/nstrftime-tests (Depends-on): Add atoll, intprops.
* tests/test-nstrftime.c: Include intprops.h, limits.h.
(errno_test): New test function.
(main): Call it.

2 files changed, 19 insertions, 2 deletions

diff --git a/lib/nstrftime.c b/lib/nstrftime.c
index 35b65bbbd6..28bc42fd66 100644
--- a/lib/nstrftime.c
+++ b/lib/nstrftime.c
@@ -33,6 +33,7 @@
 #endif
 
 #include <ctype.h>
+#include <errno.h>
 #include <time.h>
 
 #if HAVE_TZNAME && !HAVE_DECL_TZNAME
@@ -162,7 +163,10 @@ extern char *tzname[];
       size_t _w = pad == L_('-') || width < 0 ? 0 : width;                    \
       size_t _incr = _n < _w ? _w : _n;                                       \
       if (_incr >= maxsize - i)                                               \
-        return 0;                                                             \
+        {                                                                     \
+          errno = ERANGE;                                                     \
+          return 0;                                                           \
+        }                                                                     \
       if (p)                                                                  \
         {                                                                     \
           if (_n < _w)                                                        \
@@ -447,6 +451,7 @@ __strftime_internal (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
   size_t maxsize = (size_t) -1;
 #endif
 
+  int saved_errno = errno;
   int hour12 = tp->tm_hour;
 #ifdef _NL_CURRENT
   /* We cannot make the following values variables since we must delay
@@ -1186,7 +1191,13 @@ __strftime_internal (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
             time_t t;
 
             ltm = *tp;
+            ltm.tm_yday = -1;
             t = mktime_z (tz, &ltm);
+            if (ltm.tm_yday < 0)
+              {
+                errno = EOVERFLOW;
+                return 0;
+              }
 
             /* Generate string value for T using time_t arithmetic;
                this works even if sizeof (long) < sizeof (time_t).  */
@@ -1484,5 +1495,6 @@ __strftime_internal (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
     *p = L_('\0');
 #endif
 
+  errno = saved_errno;
   return i;
 }
diff --git a/lib/strftime.h b/lib/strftime.h
index e850163157..fe0c4195a5 100644
--- a/lib/strftime.h
+++ b/lib/strftime.h
@@ -24,7 +24,12 @@ extern "C" {
 /* Just like strftime, but with two more arguments:
    POSIX requires that strftime use the local timezone information.
    Use the timezone __TZ instead.  Use __NS as the number of
-   nanoseconds in the %N directive.  */
+   nanoseconds in the %N directive.
+
+   On error, set errno and return 0.  Otherwise, return the number of
+   bytes generated (not counting the trailing NUL), preserving errno
+   if the number is 0.  This errno behavior is in draft POSIX 202x
+   plus some requested changes to POSIX.  */
 size_t nstrftime (char *restrict, size_t, char const *, struct tm const *,
                   timezone_t __tz, int __ns);