Properly adjust invalid dates in RecurrenceRule enumeration (#1077)

In recurrence rules without a strict matching policy, we'd sometimes come across
dates which don't exist (such as February 29, 2009). When adjusting these dates,
we were passing unadjusted date components. That resulted in adjusted dates with
the highest unspecified component different than the original date. For example,
adjusting February 29, 2009 to match components {month: 2, day: 29} would result
February 29, 2012, instead of Match 1 or February 28 of the same year.

Adjusting the date components (that is, setting the year to 2009 for the example
above) fixes this. This is what we already do in Calendar.dates(byMatching: ...)

Author: hristost

Sources/FoundationEssentials/Calendar/Calendar_Recurrence.swift

@@ -909,7 +909,8 @@ extension Calendar {
         }
 
         let results =  try unadjustedMatchDates.map { date, components in
-            (try _adjustedDate(date, startingAfter: start, allowStartDate: true, matching: components, adjustedMatchingComponents: components , matchingPolicy: matchingPolicy, repeatedTimePolicy: repeatedTimePolicy, direction: .forward, inSearchingDate: start, previouslyReturnedMatchDate: nil), components)
+            let adjustedComponents = _adjustedComponents(components, date: start, direction: .forward)
+            return (try _adjustedDate(date, startingAfter: start, allowStartDate: true, matching: components, adjustedMatchingComponents: adjustedComponents, matchingPolicy: matchingPolicy, repeatedTimePolicy: repeatedTimePolicy, direction: .forward, inSearchingDate: start, previouslyReturnedMatchDate: nil), components)
         }
 
         var foundDates: [Date] = []

Tests/FoundationEssentialsTests/GregorianCalendarRecurrenceRuleTests.swift

@@ -426,6 +426,29 @@ final class GregorianCalendarRecurrenceRuleTests: XCTestCase {
         ]
         XCTAssertEqual(results, expectedResults)
     }
+
+    func testYearlyRecurrenceMovingToFeb29() {
+        /// Rule for an event that repeats on February 29th of each year, or closest date after
+        var rule = Calendar.RecurrenceRule(calendar: gregorian, frequency: .yearly, matchingPolicy: .nextTimePreservingSmallerComponents)
+        rule.months = [2]
+        rule.daysOfTheMonth = [29]
+
+        let rangeStart = Date(timeIntervalSince1970: 946684800.0) // 2000-01-01T00:00:00-0000
+        let rangeEnd = Date(timeIntervalSince1970: 1262304000.0) // 2010-01-01T00:00:00-0000
+        var birthdays = rule.recurrences(of: rangeStart, in: rangeStart..<rangeEnd).makeIterator()
+        //                               ^ Since the rule will change the month and day, we only borrow the time of day from the initial date
+
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 951782400.0)) // 2000-02-29T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 983404800.0)) // 2001-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1014940800.0)) // 2002-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1046476800.0)) // 2003-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1078012800.0)) // 2004-02-29T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1109635200.0)) // 2005-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1141171200.0)) // 2006-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1172707200.0)) // 2007-03-01T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1204243200.0)) // 2008-02-29T00:00:00-0000
+        XCTAssertEqual(birthdays.next(), Date(timeIntervalSince1970: 1235865600.0)) // 2009-03-01T00:00:00-0000
+    }
 
     func testYearlyRecurrenceWithMonthExpansion() {
         let start = Date(timeIntervalSince1970: 1285027200.0) // 2010-09-21T00:00:00-0000
@@ -780,5 +803,5 @@ final class GregorianCalendarRecurrenceRuleTests: XCTestCase {
             Date(timeIntervalSince1970: 1695304800.0), // 2023-09-21T14:00:00-0000
         ]
         XCTAssertEqual(results, expectedResults)
-     }
+    }
 }