Always give mktime a timeval with tm_isdst set to -1, otherwise

things get a bit out-of-phase when we step backwards 1 hour from
between 0:00 and 1:00 on the first of the month following the
transition into Summer time.  This is probably actually a bug
in mktime().

PR:	10963

If mktime() fails and 68 < year < 138, assume that the reason is
because of Summer time and adjust up or down according to our
adjusting context by one hour.  This assumes that all DSTs are
multiples of 1 hour.

PR:	6223, 17750

1 files changed, 117 insertions, 64 deletions

diff --git a/bin/date/vary.c b/bin/date/vary.c
index 97556fd..9063d38 100644
--- a/bin/date/vary.c
+++ b/bin/date/vary.c
@@ -53,6 +53,28 @@ static struct trans trans_wday[] = {
 };
 
 static char digits[] = "0123456789";
+static int adjhour(struct tm *, char, int);
+
+static int
+domktime(struct tm *t, char type)
+{
+  int ret;
+
+  /*
+   * Don't let mktime have a specific tm_isdst value.  If we do,
+   * it gets confused when we ``vary'' in and out of Summer time
+   */
+  t->tm_isdst = -1;
+  if ((ret = mktime(t)) == -1 && t->tm_year > 68 && t->tm_year < 138)
+    /*
+     * If mktime() fails, adjust by an hour.  If we're actually
+     * bridging a savings of several hours, we'll recurse several
+     * times.
+     */
+    ret = adjhour(t, type == '-' ? type : '+', 1);
+
+  return ret;
+}
 
 static int
 trans(const struct trans t[], const char *arg)
@@ -129,7 +151,7 @@ adjyear(struct tm *t, char type, int val)
         t->tm_year -= 1900;             /* struct tm holds years since 1900 */
       break;
   }
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 static int
@@ -146,12 +168,14 @@ adjmon(struct tm *t, char type, int val, int istext)
         else
           val -= t->tm_mon + 1;		/* later this year */
       }
-      if (!adjyear(t, '+', (t->tm_mon + val) / 12))
-        return 0;
-      val %= 12;
-      t->tm_mon += val;
-      if (t->tm_mon > 11)
-        t->tm_mon -= 12;
+      if (val) {
+        if (!adjyear(t, '+', (t->tm_mon + val) / 12))
+          return 0;
+        val %= 12;
+        t->tm_mon += val;
+        if (t->tm_mon > 11)
+          t->tm_mon -= 12;
+      }
       break;
 
     case '-':
@@ -161,15 +185,17 @@ adjmon(struct tm *t, char type, int val, int istext)
         else
           val = t->tm_mon - val + 1;	/* early this year */
       }
-      if (!adjyear(t, '-', val / 12))
-        return 0;
-      val %= 12;
-      if (val > t->tm_mon) {
-        if (!adjyear(t, '-', 1))
+      if (val) {
+        if (!adjyear(t, '-', val / 12))
           return 0;
-        val -= 12;
+        val %= 12;
+        if (val > t->tm_mon) {
+          if (!adjyear(t, '-', 1))
+            return 0;
+          val -= 12;
+        }
+        t->tm_mon -= val;
       }
-      t->tm_mon -= val;
       break;
 
     default:
@@ -178,13 +204,14 @@ adjmon(struct tm *t, char type, int val, int istext)
       t->tm_mon = --val;
   }
 
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 static int
 adjday(struct tm *t, char type, int val)
 {
   int mdays;
+
   switch (type) {
     case '+':
       while (val) {
@@ -221,7 +248,7 @@ adjday(struct tm *t, char type, int val)
       break;
   }
 
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 static int
@@ -238,17 +265,17 @@ adjwday(struct tm *t, char type, int val, int istext)
         else
           val -= t->tm_wday;           /* later this week */
       else
-        val *= 7;                      /* "-W +5" == "5 weeks in the future" */
-      return adjday(t, '+', val);
+        val *= 7;                      /* "-v+5w" == "5 weeks in the future" */
+      return !val || adjday(t, '+', val);
     case '-':
-      if (istext)
+      if (istext) {
         if (val > t->tm_wday)
           val = 7 - val + t->tm_wday;  /* later last week */
         else
           val = t->tm_wday - val;      /* early this week */
-      else
-        val *= 7;                      /* "-W -5" == "5 weeks ago" */
-      return adjday(t, '-', val);
+      } else
+        val *= 7;                      /* "-v-5w" == "5 weeks ago" */
+      return !val || adjday(t, '-', val);
     default:
       if (val < t->tm_wday)
         return adjday(t, '-', t->tm_wday - val);
@@ -263,29 +290,47 @@ adjwday(struct tm *t, char type, int val, int istext)
 static int
 adjhour(struct tm *t, char type, int val)
 {
+  /*
+   * We've got to be careful here in case
+   *   domktime() calls
+   *   adjhour() calls
+   *   adjday() calls
+   *   domktime() calls
+   *   adjhour() and recurses forever.  It's vital that we've adjusted our
+   *   number of hours before calling adjday().
+   */
+
   if (val < 0)
     return 0;
 
   switch (type) {
     case '+':
-      if (!adjday(t, '+', (t->tm_hour + val) / 24))
-        return 0;
-      val %= 24;
-      t->tm_hour += val;
-      if (t->tm_hour > 23)
-        t->tm_hour -= 24;
+      if (val) {
+        int days;
+
+        days = (t->tm_hour + val) / 24;
+        val %= 24;
+        t->tm_hour += val;
+        t->tm_hour %= 24;
+        if (!adjday(t, '+', days))
+          return 0;
+      }
       break;
 
     case '-':
-      if (!adjday(t, '-', val / 24))
-        return 0;
-      val %= 24;
-      if (val > t->tm_hour) {
-        if (!adjday(t, '-', 1))
+      if (val) {
+        int days;
+
+        days = val / 24;
+        val %= 24;
+        if (val > t->tm_hour) {
+          days++;
+          val -= 24;
+        }
+        t->tm_hour -= val;
+        if (!adjday(t, '-', val / 24))
           return 0;
-        val -= 24;
       }
-      t->tm_hour -= val;
       break;
 
     default:
@@ -294,7 +339,7 @@ adjhour(struct tm *t, char type, int val)
       t->tm_hour = val;
   }
 
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 static int
@@ -305,24 +350,28 @@ adjmin(struct tm *t, char type, int val)
 
   switch (type) {
     case '+':
-      if (!adjhour(t, '+', (t->tm_min + val) / 60))
-        return 0;
-      val %= 60;
-      t->tm_min += val;
-      if (t->tm_min > 59)
-        t->tm_min -= 60;
+      if (val) {
+        if (!adjhour(t, '+', (t->tm_min + val) / 60))
+          return 0;
+        val %= 60;
+        t->tm_min += val;
+        if (t->tm_min > 59)
+          t->tm_min -= 60;
+      }
       break;
 
     case '-':
-      if (!adjhour(t, '-', val / 60))
-        return 0;
-      val %= 60;
-      if (val > t->tm_min) {
-        if (!adjhour(t, '-', 1))
+      if (val) {
+        if (!adjhour(t, '-', val / 60))
           return 0;
-        val -= 60;
+        val %= 60;
+        if (val > t->tm_min) {
+          if (!adjhour(t, '-', 1))
+            return 0;
+          val -= 60;
+        }
+        t->tm_min -= val;
       }
-      t->tm_min -= val;
       break;
 
     default:
@@ -331,7 +380,7 @@ adjmin(struct tm *t, char type, int val)
       t->tm_min = val;
   }
 
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 static int
@@ -342,24 +391,28 @@ adjsec(struct tm *t, char type, int val)
 
   switch (type) {
     case '+':
-      if (!adjmin(t, '+', (t->tm_sec + val) / 60))
-        return 0;
-      val %= 60;
-      t->tm_sec += val;
-      if (t->tm_sec > 59)
-        t->tm_sec -= 60;
+      if (val) {
+        if (!adjmin(t, '+', (t->tm_sec + val) / 60))
+          return 0;
+        val %= 60;
+        t->tm_sec += val;
+        if (t->tm_sec > 59)
+          t->tm_sec -= 60;
+      }
       break;
 
     case '-':
-      if (!adjmin(t, '-', val / 60))
-        return 0;
-      val %= 60;
-      if (val > t->tm_sec) {
-        if (!adjmin(t, '-', 1))
+      if (val) {
+        if (!adjmin(t, '-', val / 60))
           return 0;
-        val -= 60;
+        val %= 60;
+        if (val > t->tm_sec) {
+          if (!adjmin(t, '-', 1))
+            return 0;
+          val -= 60;
+        }
+        t->tm_sec -= val;
       }
-      t->tm_sec -= val;
       break;
 
     default:
@@ -368,7 +421,7 @@ adjsec(struct tm *t, char type, int val)
       t->tm_sec = val;
   }
 
-  return mktime(t) != -1;
+  return domktime(t, type) != -1;
 }
 
 const struct vary *