FA-77147 / Calendar recurrence rules / Member archive

Monthly day 29-31 with OMIT/BACKWARD/FORWARD skip policy: backward target · case 02

BACKWARD from the 31st lands on the 28th of 30-day months.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

FREQ=MONTHLY on a fixed monthday from the dtstart month. When the day does not exist in a month, skip decides: OMIT (also the default when skip is None) drops the month, BACKWARD uses the last day of the month, FORWARD uses the first day of the following month. February has 29 days in leap years. Instances before dtstart are dropped. Return the first count ISO dates.

Why this case matters

Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
backward from 31st	`["2024-03-31", "2024-04-28", "2024-05-31", "2024-06-28"]`	`["2024-03-31", "2024-04-30", "2024-05-31", "2024-06-30"]`	Failed

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