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fix Calendar.RecurrenceRule #1284

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fix Calendar.RecurrenceRule #1284

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12 changes: 12 additions & 0 deletions Sources/FoundationEssentials/Calendar/Calendar_Recurrence.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,9 @@ extension Calendar {
/// value is used as a lower bound for ``nextBaseRecurrenceDate()``.
let rangeLowerBound: Date?

/// The start date's nanoseconds component
let startDateNanoseconds: TimeInterval

/// How many occurrences have been found so far
var resultsFound = 0

Expand Down Expand Up @@ -232,6 +235,8 @@ extension Calendar {
}
var componentsForEnumerating = recurrence.calendar._dateComponents(components, from: start)

startDateNanoseconds = start.timeIntervalSince1970.remainder(dividingBy: 1)
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Would it work if we modify components above to include nanoseconds so the information is readily available in componentsForEnumerating, so that we don't have to do this manual adjustment here?

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@itingliu that was my first attempt, but it doesn't work.

in my understanding, the issue is that Calendar.DatesByRecurring's underlying baseRecurrence (Calendar.DatesByMatching) will always return only whole-second-rounded dates (though this isn't documented, afaict), so we'd need to adjust that type's behaviour instead (which i decided against bc i wasn't sure whether this would affect any other dependent code, and i figured instead going with the simplest possible fix would be the best approach)


let expansionChangesDay = dayOfYearAction == .expand || dayOfMonthAction == .expand || weekAction == .expand || weekdayAction == .expand
let expansionChangesMonth = dayOfYearAction == .expand || monthAction == .expand || weekAction == .expand

Expand Down Expand Up @@ -422,6 +427,13 @@ extension Calendar {
recurrence._limitTimeComponent(.second, dates: &dates, anchor: anchor)
}

if startDateNanoseconds > 0 {
// `_dates(startingAfter:)` above returns whole-second dates,
// so we need to restore the nanoseconds value present in the original start date.
for idx in dates.indices {
dates[idx] += startDateNanoseconds
}
}
dates = dates.filter { $0 >= self.start }

if let limit = recurrence.end.date {
Expand Down
12 changes: 12 additions & 0 deletions Tests/FoundationEssentialsTests/GregorianCalendarRecurrenceRuleTests.swift
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Expand Up @@ -803,4 +803,16 @@ final class GregorianCalendarRecurrenceRuleTests: XCTestCase {
]
XCTAssertEqual(results, expectedResults)
}

func testDailyRecurrenceRuleWithNonzeroNanosecondComponent() {
let start = Date(timeIntervalSince1970: 1746627600.5) // 2025-05-07T07:20:00.500-07:00
let rule = Calendar.RecurrenceRule.daily(calendar: gregorian, end: .afterOccurrences(2))
let results = Array(rule.recurrences(of: start))

let expectedResults: [Date] = [
start,
Date(timeIntervalSince1970: 1746714000.5), // 2025-05-08T07:20:00.500-07:00
]
XCTAssertEqual(results, expectedResults)
}
}