More fixes:

- DateComponent should only return isLeapMonth if the underlying leapMonthSet variable is true. Previously, DateComponent was setting isLeapMonth to false in situations where there is no concept of isLeapMonth.
- _convert was using 'L' for isLeapMonth, when the corresponding UCalendarDateFields enum value for isLeapMonth is 'l'. This was causing _CFCalendarAddComponentsV to return error status.

Author: Jason Ji

Foundation/DateComponents.swift

@@ -189,7 +189,7 @@ public struct DateComponents : ReferenceConvertible, Hashable, Equatable, _Mutab
 
     /// Set to true if these components represent a leap month.
     public var isLeapMonth: Bool? {
-        get { return _handle.map { $0.isLeapMonth } }
+        get { return _handle.map { $0.leapMonthSet ? $0.isLeapMonth : nil } }
         set {
             _applyMutation {
                 // Technically, the underlying class does not support setting isLeapMonth to nil, but it could - so we leave the API consistent.

Foundation/NSCalendar.swift

@@ -461,7 +461,7 @@ open class NSCalendar : NSObject, NSCopying, NSSecureCoding {
         _convert(comps.weekday, type: "E", vector: &vector, compDesc: &compDesc)
         _convert(comps.weekdayOrdinal, type: "F", vector: &vector, compDesc: &compDesc)
         _convert(comps.month, type: "M", vector: &vector, compDesc: &compDesc)
-        _convert(comps.isLeapMonth, type: "L", vector: &vector, compDesc: &compDesc)
+        _convert(comps.isLeapMonth, type: "l", vector: &vector, compDesc: &compDesc)
         _convert(comps.day, type: "d", vector: &vector, compDesc: &compDesc)
         _convert(comps.hour, type: "H", vector: &vector, compDesc: &compDesc)
         _convert(comps.minute, type: "m", vector: &vector, compDesc: &compDesc)

TestFoundation/TestNSCalendar.swift

@@ -92,14 +92,15 @@ class TestNSCalendar: XCTestCase {
     }
 
     func test_addingDates() {
-        var calendar = Calendar.current
-        let today = calendar.current.date(from: DateComponents(year: 2016, month: 10, day: 4))
+        let calendar = Calendar.current
+        let today = Date()
         let diffComponents = DateComponents(day: 1)
         let tomorrow = calendar.date(byAdding: diffComponents, to: today)
 
-        XCTAssertEqual(tomorrow.year, 2016)
-        XCTAssertEqual(tomorrow.month, 10)
-        XCTAssertEqual(tomorrow.day, 5)
+        let tomorrowComponents = calendar.dateComponents([.year, .month, .day], from: tomorrow!)
+        XCTAssertEqual(tomorrowComponents.year, 2016)
+        XCTAssertEqual(tomorrowComponents.month, 10)
+        XCTAssertEqual(tomorrowComponents.day, 5)
     }
 }