[BUG] - ErrAtTimeNotSupported when trying to Update/reschedule Job

[calvinmclean]

Describe the bug

When attempting to reschedule a Job originally scheduled with Every(time.Duration) by setting a new StartAt time (to delay 24 hours), ErrAtTimeNotSupported is returned. It's unexpected because I used StartAt on the original scheduling so the re-schedule isn't doing anything different.

I'm not 100% sure this is a bug or intentional behavior, but I started getting this error after updating from v1.18.1.

To Reproduce

Reproducible with this test:

func TestGoCron(t *testing.T) {
	s := gocron.NewScheduler(time.Local)
	s.StartAsync()
	defer s.Stop()

	startDate, err := time.Parse(time.RFC3339, "2022-04-23T22:00:00-07:00")
	assert.NoError(t, err)

	_, err = s.
		Every(24*time.Hour).
		StartAt(startDate).
		Tag("TAG_ID").
		Do(fmt.Println, "Hello!")
	assert.NoError(t, err)

	sort.Sort(s)
	jobs, err := s.FindJobsByTag("TAG_ID")
	assert.NoError(t, err)
	assert.Len(t, jobs, 1)

	nextRun := jobs[0].NextRun()
	newNextRun := nextRun.Add(24 * time.Hour)

	newJob, err := s.Job(jobs[0]).
		StartAt(newNextRun).
		Update()
	assert.NoError(t, err)
	if newJob != nil {
		assert.Equal(t, newNextRun, newJob.NextRun())
	}
}

Version

v1.28.0

Expected behavior

Expectations are shown in the above test code: no error and job is rescheduled for 24 hours in the future.

Additional context

The error is coming from here.
In both the original scheduling and re-scheduling, jobUnit is duration. In original schedule, job.getAtTime(jobLastRun) is 0, so there is no error. When rescheduling, this is a non-zero value and it errors.

[calvinmclean]

I just tried changing Every(24 * time.Hour) to Every(1).Day() and now it works as expected, so I at least have a workaround.
However, if you review this and think it sounds like a real bug, I can create a PR to fix it if you are able to give a little background info on what is the issue :)

[JohnRoesler]

I believe it’s a bug. I’ll take a deeper look later this week. A pr would of course be appreciated!

[JohnRoesler]

I found the issue. I'll have a PR up this week

[calvinmclean]

I found the issue. I'll have a PR up this week

Thanks for the quick fix! 🙂