FA-76948 / Calendar recurrence rules / Member archive

Yearly BYMONTH/BYMONTHDAY with leap-day skipping: interval anchor · case 03

An every-other-year series whose first-year date precedes dtstart runs in the wrong year parity.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

FREQ=YEARLY on a fixed month and day. Years are dtstart.year + k*interval. A year in which the date does not exist (for example February 29 in a common year) is skipped, never clamped. Gregorian leap years: divisible by 4, except centuries not divisible by 400. Instances before dtstart are dropped and the series ends at until (inclusive). Return 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
interval 4 leap-day from 2023	`["2024-02-29", "2028-02-29", "2032-02-29", "2036-02-29", "2040-02-29"]`	`[]`	Failed

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