FA-76937 / Calendar recurrence rules / Member archive

Monthly BYSETPOS selection from a weekday set: emit order · case 02

BYSETPOS=-1,1 emits the last day before the first, and COUNT keeps the wrong instance.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

FREQ=MONTHLY;BYDAY=<weekdays>;BYSETPOS=<positions>. For each month from the dtstart month, the candidate set is every day of the whole month whose weekday is listed, in date order. Positions are 1-based, negative from the end; out-of-range positions are ignored and positions naming the same day yield it once. Selected days are emitted chronologically; days before dtstart are dropped after selection. 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
first and last in reverse order	`["2024-03-29", "2024-03-01", "2024-04-30", "2024-04-01"]`	`["2024-03-01", "2024-03-29", "2024-04-01", "2024-04-30"]`	Failed

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