Don't skip crons when time jumps fwd due to DST

Author: rdingwall

spec.go

@@ -135,13 +135,25 @@ WRAP:
 		}
 	}
 
+HOUR:
 	for 1<<uint(t.Hour())&s.Hour == 0 {
 		if !added {
 			added = true
 			t = time.Date(t.Year(), t.Month(), t.Day(), t.Hour(), 0, 0, 0, loc)
 		}
+		prev := t
 		t = t.Add(1 * time.Hour)
-
+		// Special handling to avoid skipped crons when time jumps forward due
+		// to DST. E.g. if time jumps from 1:59 to 3:00, a 2:00 cron should get
+		// triggered at 3:00. To do this we calculate how many hours were
+		// skipped after calling t.Add(1 * time.Hour), then we check each
+		// skipped hour to see if it was set in the bitmap.
+		step := t.Hour() - prev.Hour()
+		for i := 1; i < step; i++ {
+			if 1<<uint(t.Hour()-i)&s.Hour > 0 {
+				break HOUR
+			}
+		}
 		if t.Hour() == 0 {
 			goto WRAP
 		}

spec_test.go

@@ -111,7 +111,7 @@ func TestNext(t *testing.T) {
 		{"Mon Jul 9 23:35 2012", "0 0 0 29 Feb ?", "Mon Feb 29 00:00 2016"},
 
 		// Daylight savings time 2am EST (-5) -> 3am EDT (-4)
-		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 30 2 11 Mar ?", "2013-03-11T02:30:00-0400"},
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 30 2 11 Mar ?", "2012-03-11T03:30:00-0400"},
 
 		// hourly job
 		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T01:00:00-0500"},
@@ -129,8 +129,8 @@ func TestNext(t *testing.T) {
 		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-11T01:00:00-0500"},
 		{"2012-03-11T01:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-12T01:00:00-0400"},
 
-		// 2am nightly job (skipped)
-		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-03-12T02:00:00-0400"},
+		// Daylight savings time 2am EST (-5) -> 3am EDT (-4)
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-03-11T03:00:00-0400"},
 
 		// Daylight savings time 2am EDT (-4) => 1am EST (-5)
 		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 30 2 04 Nov ?", "2012-11-04T02:30:00-0500"},