chore: improve access to default fields in cron parser (#5750)

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: memoclaw <265580040+memoclaw@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

plugin/cron/cron_test.go

@@ -627,28 +627,31 @@ func TestStopAndWait(t *testing.T) {
 	t.Run("repeated calls to stop, waiting for completion and after", func(*testing.T) {
 		cron := newWithSeconds()
 		cron.AddFunc("* * * * * *", func() {})
-		cron.AddFunc("* * * * * *", func() { time.Sleep(2 * time.Second) })
+		cron.AddFunc("* * * * * *", func() { time.Sleep(3 * time.Second) })
 		cron.Start()
 		cron.AddFunc("* * * * * *", func() {})
 		time.Sleep(time.Second)
 		ctx := cron.Stop()
 		ctx2 := cron.Stop()
 
-		// Verify that it is not done for at least 1500ms
+		// Verify that it is not done for at least 1500ms.
+		// The 3-second sleep job starts within 1s of cron.Start(), so it always has
+		// at least 2s remaining when Stop() is called, well above this threshold.
 		select {
 		case <-ctx.Done():
 			t.Error("context was done too quickly immediately")
 		case <-ctx2.Done():
 			t.Error("context2 was done too quickly immediately")
 		case <-time.After(1500 * time.Millisecond):
-			// expected, because the job sleeping for 2 seconds is still running
+			// expected, because the job sleeping for 3 seconds is still running
 		}
 
-		// Verify that it IS done in the next 1s (giving 500ms buffer)
+		// Verify that it IS done in the next 2s (giving 500ms buffer).
+		// After the 1500ms wait above, at most 1500ms of the job remain.
 		select {
 		case <-ctx.Done():
 			// expected
-		case <-time.After(time.Second):
+		case <-time.After(2 * time.Second):
 			t.Error("context not done after job should have completed")
 		}
 

plugin/cron/parser.go

@@ -27,6 +27,15 @@ const (
 	Descriptor                             // Allow descriptors such as @monthly, @weekly, etc.
 )
 
+const (
+	secondIndex = iota
+	minuteIndex
+	hourIndex
+	domIndex
+	monthIndex
+	dowIndex
+)
+
 var places = []ParseOption{
 	Second,
 	Minute,
@@ -193,9 +202,9 @@ func normalizeFields(fields []string, options ParseOption) ([]string, error) {
 	if min < max && len(fields) == min {
 		switch {
 		case options&DowOptional > 0:
-			fields = append(fields, defaults[5]) // TODO: improve access to default
+			fields = append(fields, defaults[dowIndex])
 		case options&SecondOptional > 0:
-			fields = append([]string{defaults[0]}, fields...)
+			fields = append([]string{defaults[secondIndex]}, fields...)
 		default:
 			return nil, errors.New("unexpected optional field")
 		}