FA-76845 / Calendar recurrence rules / Member archive

Weekly BYDAY expansion honouring the week-start day: week anchor · case 05

With a Sunday week start and INTERVAL=2, the active weeks are shifted so Sunday instances land in the skipped week.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

FREQ=WEEKLY expansion. byday lists weekday numbers (0=Monday..6=Sunday); an empty list means the weekday of dtstart. Weeks begin on wkst; the week containing dtstart is week 0 and only weeks whose index is a multiple of interval are active. Instances are chronological, never before dtstart, and dtstart itself is an instance only if its weekday is listed. 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
WKST=WE interval 2 MO,TH	`["2024-06-04", "2024-06-08", "2024-06-18", "2024-06-22", "2024-07-02"]`	`["2024-06-13", "2024-06-17", "2024-06-27", "2024-07-01", "2024-07-11"]`	Failed

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