Recurrence with frequency YEARLY and specifying rule BYMONTHDAY is not function as expected

[jorgegiro]

Hi!

I starting to using the library in order to calculate recurrent dates. And I try to set a Recurrence specifying a frequency of YEARLY and only setting a rule of BYMONTHDAY. For example, I am trying to calculate:

    StartDate : 2021/01/01
    Until: DateTime.MaxValue
    Frequency: Yearly
    Interval: 1
    ByMonthDay: 3

var recurrence = new Recurrence();
recurrence.StartDateTime =new DateTime(2021, 01, 01);
recurrence.RecurUntil = DateTime.MaxValue;
recurrence.Frequency = RecurFrequency.Yearly;
recurrence.Interval = 1;
recurrence.ByMonthDay.Add(3);

DateTime nextDate = recurrence.NextInstance(new DateTime(2021, 01, 10), false);

Then, what I expect when NextInstance(new DateTime(2021, 01, 10), false) it is called it is a return date 2022/01/03. But instead, it's returning '2022/01/01'.

This is happening because when expanding dates, expand ByMonthDate and if its not set ByWeekNo expands ByDay even it's not set any ByDay rule. This cause, that a RecurDateTimeCollection is genarated containing the date 2022/01/01 and is included as an instance.

if(byMonthDay.Count != 0)
{
    // Expand by month day if specified without any by month rule part
    isExpanded = true;
    rdtcMoDay = new RecurDateTimeCollection(dates);
    freqRules.ByMonthDay(this, rdtcMoDay);
}

// As long as by week number isn't specified either, we'll expand the by day rule here too
if(byWeekNo.Count == 0)
{
   isExpanded = true;
   rdtcDay = new RecurDateTimeCollection(dates);
   freqRules.ByDay(this, rdtcDay);
}

Please, Could you confirm if this is the right behaviour? Or may be NextInstance should return 2022/01/03? Or may be I am setting something wrong. It's also possible 😅

[EWSoftware]

Yes, I think it is being applied incorrectly in this case. If you add a BYMONTH=1 condition, you do get the results you'd expect. Since a BYMONTHDAY condition is being specified, it shouldn't be pulling in the day from the start date and should be expanding it using only the BYMONTHDAY values.

[EWSoftware]

I merged the change. It will be in the next release due out soon.