CronTab.floor / .ceil should return times at minute granularity

[jglick]

f97b5b3 seems to have been calling previously unused utility methods.

jenkins/core/src/main/java/hudson/triggers/Trigger.java

Lines 223 to 224 in 630b6b6

	cal.set(Calendar.SECOND, 0);
	cal.set(Calendar.MILLISECOND, 0);

(#1216) shows how the actual trigger is checked at precise one-minute intervals, and

jenkins/core/src/main/java/hudson/scheduler/CronTab.java

Lines 160 to 169 in 630b6b6

	if (!checkBits(bits[0], checkCal.get(MINUTE)))
	return false;
	if (!checkBits(bits[1], checkCal.get(HOUR_OF_DAY)))
	return false;
	if (!checkBits(bits[2], checkCal.get(DAY_OF_MONTH)))
	return false;
	if (!checkBits(bits[3], checkCal.get(MONTH) + 1))
	return false;
	if (!checkBits(dayOfWeek, checkCal.get(Calendar.DAY_OF_WEEK) - 1))
	return false;

does not even consider seconds or microseconds, so the form validation rendered at 2:17:23 would claim that */5 * * * * would next run at 2:20:23, which is not really true: it would run at 2:20:00, or very shortly thereafter, and at any rate not specifically at 23 seconds past the minute.

Testing done

Unit tests, and then some interactive sanity checks of form validation including of @hourly etc.

Proposed changelog entries

• Form validation for cron schedules included seconds based on the current time, when in fact the trigger fires at minute-granularity slots.

Proposed upgrade guidelines

N/A

Desired reviewers

@Vlatombe

Before the changes are marked as ready-for-merge:

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[jglick]

Beware that floor and ceil mutate their argument.

[MarkEWaite]

This PR is now ready for merge. We will merge it after approximately 24 hours if there is no negative feedback.

/label ready-for-merge

[A1exKH]

@jglick LGTM.