libast/tm: DST offset and contemporaneous time zone fixes.

src/cmd/ksh93/tests/attributes.sh

@@ -362,9 +362,9 @@ $SHELL -c 'builtin date' >/dev/null 2>&1 &&
 # check env var changes against a builtin that uses the env var
 
 SEC=1234252800
-ETZ=EST5EDT
+ETZ=EST5EDT,M3.2.0/2:00:00,M11.1.0/2:00:00
 EDT=03
-PTZ=PST8PDT
+PTZ=PST8PDT,M3.2.0/2:00:00,M11.1.0/2:00:00
 PDT=00
 
 CMD="date -f%H \\#$SEC"

src/cmd/ksh93/tests/printf.sh

@@ -211,14 +211,62 @@ function do_test # 1:LINENO 2:printf-STRING 3:match-string
 }
 
 # The first tests require a time zone with one or more historical changes.
-format='%Y-%m-%d %H:%M:%S'
-export TZ=Europe/Riga
-
 C='Historical changes (bad time)' # https://github.com/ksh93/ksh/issues/669
+export TZ=Europe/Riga
+format='%Y-%m-%d %H:%M:%S'
 T '#236961303'				'1977-07-05 17:35:03'
+format='%s'
+T '1977-07-05 17:35:03'		'236961303'
 
 export TZ=Europe/London
+format='%Y-%m-%d %H:%M:%S'
 T '#0'					'1970-01-01 01:00:00'
+format='%s'
+T '1970-01-01 01:00:00'		'0'
+
+C='Before and after a historical change (bad time)'
+export TZ=Pacific/Apia
+format='%Y-%m-%d %H:%M:%S'
+T '#1325239200'			'2011-12-31 00:00:00'
+T '#1325239199'			'2011-12-29 23:59:59'
+format='%s'
+T '2011-12-31 00:00:00'		'1325239200'
+T '2011-12-29 23:59:59'		'1325239199'
+
+C='Historical change from one DST zone to another (bad time)'
+export TZ=Europe/Chisinau
+format='%Y-%m-%d %H:%M:%S'
+T '#642286800'				'1990-05-10 00:00:00'
+format='%s'
+T '1990-05-10 00:00:00'		'642286800'
+
+C='Historical change from DST to standard (bad time)'
+export TZ=America/Indiana/Knox
+format='%Y-%m-%d %H:%M:%S'
+T '#688626000'				'1991-10-28 00:00:00'
+format='%s'
+T '1991-10-28 00:00:00'		'688626000'
+
+C='Historical change from standard to DST (bad time)'
+export TZ=America/Kentucky/Louisville
+format='%Y-%m-%d %H:%M:%S'
+T '#126766800'				'1974-01-07 00:00:00'
+format='%s'
+T '1974-01-07 00:00:00'		'126766800'
+
+C='Historical change from standard to standard (bad time)'
+export TZ=America/Argentina/San_Juan
+format='%Y-%m-%d %H:%M:%S'
+T '#1086148800'			'2004-06-02 00:00:00'
+format='%s'
+T '2004-06-02 00:00:00'		'1086148800'
+
+C='POSIX timezone strings without rules (bad time, musl)' #https://github.com/ksh93/ksh/issues/976
+export TZ=EST5EDT
+format='%Y-%m-%d %H:%M:%S'
+T '#1274252800'			'2010-05-19 03:06:40'
+format='%s'
+T '2010-05-19 03:06:40'		'1274252800'
 
 format='%Y-%m-%d'
 export TZ=UTC

src/lib/libast/tm/tminit.c

@@ -196,6 +196,8 @@ tmlocal(time_t now)
 	char*			e = NULL;
 	int			i;
 	int			m;
+	int			o;
+	int			p;
 	int			isdst;
 	char*			t;
 	struct tm*		tp;
@@ -237,27 +239,38 @@ tmlocal(time_t now)
 
 	tm_info.zone = tm_info.local = &local;
 	n = tzwest(&now, &isdst);
+	p = n;
+	o = isdst;
 
 	/*
 	 * compute local DST offset by roaming
 	 * through the last 12 months until tzwest() changes
+	 * with a system-recognized DST change
 	 */
 
 	for (i = 0; i < 12; i++)
 	{
 		now -= 31 * 24 * 60 * 60;
-		if ((m = tzwest(&now, &isdst)) != n)
+		if ((m = tzwest(&now, &isdst)) != n && ((!isdst && o) || (isdst && !o)))
 		{
+			m -= (n - p);
+			n = p;
 			if (!isdst)
 			{
-				isdst = n;
 				n = m;
-				m = isdst;
+				m = p;
 			}
-			m -= n;
 			break;
 		}
+		n = m;
+		if (i == 11)
+		{
+			n = p;
+			m = n;
+		}
 	}
+	m -= n;
+	isdst = o;
 	local.west = (short)n;
 	local.dst = (short)m;
 

src/lib/libast/tm/tmxdate.c

@@ -172,6 +172,11 @@ tmxdate(const char* s, char** e, Time_t now)
 	int		dir;
 	int		dst;
 	int		zone;
+	int		dst_old;
+	int		west_old;
+	int		isdst_old;
+	int		first = 1;
+	int		good_check = 0;
 	int		c;
 	int		f;
 	int		i;
@@ -206,7 +211,13 @@ tmxdate(const char* s, char** e, Time_t now)
 	 */
 
 	tm = tmxtm(&ts, now, NULL, 1);
+	if (!first && dst_old == tm->tm_zone->dst && west_old == tm->tm_zone->west && isdst_old == tm->tm_isdst)
+		good_check = 1;
+	dst_old = tm->tm_zone->dst;
+	west_old = tm->tm_zone->west;
+	isdst_old = tm->tm_isdst;
 	tm_info.date = tm->tm_zone;
+	first = 0;
 	day = -1;
 	dir = 0;
 	dst = TM_DST;
@@ -1779,6 +1790,15 @@ tmxdate(const char* s, char** e, Time_t now)
 			tm->tm_mday += j;
 		}
 	}
+	tm = tmxtm(tm, tmxtime(tm, zone), tm->tm_zone, 1);
+	if (!first)
+	{
+		int offset = tm->tm_zone->west - west_old;
+		if (tm->tm_isdst)
+			offset += tm->tm_zone->dst - dst_old;
+		tm->tm_min += offset;
+		tmfix(tm);
+	}
 	now = tmxtime(tm, zone);
 	if (tm->tm_year <= 70 && tmxsec(now) > 31536000)
 	{
@@ -1787,5 +1807,7 @@ tmxdate(const char* s, char** e, Time_t now)
 	}
 	if (e)
 		*e = last;
+	if (!good_check)
+		goto reset;
 	return now;
 }