Swift 向后枚举时枚举日期是否存在差异？

在向前或向后两个日期之间枚举一个月中的一天时，会出现一个奇怪的差异。向前枚举时，我得到了正确的答案，但向后枚举时，枚举日期会莫名其妙地跳跃

让我们尝试列举2020年和1980年之间的日期：

let cal = Calendar.current
var dateComponents = DateComponents()
dateComponents.year = 1980
dateComponents.month = 1
dateComponents.day = 1
dateComponents.timeZone = TimeZone(abbreviation: "CET")
dateComponents.hour = 8
dateComponents.minute = 0
let stopDate = cal.date(from: dateComponents)
dateComponents.year = 2020
dateComponents.month = 1
dateComponents.day = 1
let startDate = cal.date(from: dateComponents)
if let stopDate = stopDate {
    if let startDate = startDate {
        var comps = DateComponents()

        //Lets enumerate forward first

        print("Enumerating forward")
        for dotm in 1..<32 {
            var counter = 0
            comps.day = dotm
            comps.hour = 8
            cal.enumerateDates(startingAfter: stopDate, matching: comps, matchingPolicy: .strict, repeatedTimePolicy: .first, direction: .forward) { (date, match, stop) in
                if let date = date {
                    counter += 1
                    if date > startDate {
                        print("number of months with day \(dotm) in month: \(counter)")
                        counter = 0
                        stop = true
                    }
                }
            }
        }

        //And do the same thing backward

        print("Enumerating backward")
        for dotm in 1..<32 {
            var counter = 0
            comps.day = dotm
            comps.hour = 8
            cal.enumerateDates(startingAfter: startDate, matching: comps, matchingPolicy: .strict, repeatedTimePolicy: .first, direction: .backward) { (date, match, stop) in
                if let date = date {
                    counter += 1
                    if date < stopDate {
                        print("number of months with day \(dotm) in month: \(counter)")
                        counter = 0
                        stop = true
                    }
                }
            }
        }

        //Lets inspect closer

        print("What is happening?")
        comps.day = 1
        cal.enumerateDates(startingAfter: startDate, matching: comps, matchingPolicy: .strict, repeatedTimePolicy: .first, direction: .backward) { (date, match, stop) in
            if let date = date {
                print("Date found: \(date)")
                if date < stopDate {
                    stop = true
                }
            }
        }
    }
}

从2019年到1995年，再从1980年到1976年，倒数出现了一个奇怪的跳跃。我是做错了什么，还是这是一个错误？我使用的是Xcode 11.3

更新：

向后枚举时枚举日期的行为更为奇怪。当我们更改起始日期时，计数有时是正确的。快速检查2020年1月的所有可能开始日，我们得到以下矩阵（第一列为startDate，第二列为dateComponents.day=1的天数，第三列为dateComponents.day=2，以此类推）

---

因此，如果第一次命中的日期是在当前月份，那么枚举日期可能才正确计数？

这是一个错误，它总是在日期设置为10月1日之后发生

请像我几周前做的那样提交bug，不幸的是苹果还没有回应

Enumerating forward
number of months with day 1 in month: 481
number of months with day 2 in month: 481
number of months with day 3 in month: 481
number of months with day 4 in month: 481
number of months with day 5 in month: 481
number of months with day 6 in month: 481
number of months with day 7 in month: 481
number of months with day 8 in month: 481
number of months with day 9 in month: 481
number of months with day 10 in month: 481
number of months with day 11 in month: 481
number of months with day 12 in month: 481
number of months with day 13 in month: 481
number of months with day 14 in month: 481
number of months with day 15 in month: 481
number of months with day 16 in month: 481
number of months with day 17 in month: 481
number of months with day 18 in month: 481
number of months with day 19 in month: 481
number of months with day 20 in month: 481
number of months with day 21 in month: 481
number of months with day 22 in month: 481
number of months with day 23 in month: 481
number of months with day 24 in month: 481
number of months with day 25 in month: 481
number of months with day 26 in month: 481
number of months with day 27 in month: 481
number of months with day 28 in month: 481
number of months with day 29 in month: 451
number of months with day 30 in month: 441
number of months with day 31 in month: 281
Enumerating backward
number of months with day 1 in month: 189
number of months with day 2 in month: 189
number of months with day 3 in month: 189
number of months with day 4 in month: 189
number of months with day 5 in month: 189
number of months with day 6 in month: 189
number of months with day 7 in month: 189
number of months with day 8 in month: 189
number of months with day 9 in month: 189
number of months with day 10 in month: 189
number of months with day 11 in month: 189
number of months with day 12 in month: 189
number of months with day 13 in month: 189
number of months with day 14 in month: 189
number of months with day 15 in month: 189
number of months with day 16 in month: 189
number of months with day 17 in month: 189
number of months with day 18 in month: 189
number of months with day 19 in month: 189
number of months with day 20 in month: 189
number of months with day 21 in month: 189
number of months with day 22 in month: 189
number of months with day 23 in month: 189
number of months with day 24 in month: 189
number of months with day 25 in month: 189
number of months with day 26 in month: 189
number of months with day 27 in month: 189
number of months with day 28 in month: 189
number of months with day 29 in month: 177
number of months with day 30 in month: 174
number of months with day 31 in month: 111
What is happening?
Date found: 2019-12-01 07:00:00 +0000
Date found: 2019-11-01 07:00:00 +0000
Date found: 2019-10-01 06:00:00 +0000
Date found: 1995-09-01 06:00:00 +0000
Date found: 1995-08-01 06:00:00 +0000
Date found: 1995-07-01 06:00:00 +0000
Date found: 1995-06-01 06:00:00 +0000
Date found: 1995-05-01 06:00:00 +0000
Date found: 1995-04-01 06:00:00 +0000
Date found: 1995-03-01 07:00:00 +0000
Date found: 1995-02-01 07:00:00 +0000
Date found: 1995-01-01 07:00:00 +0000
Date found: 1994-12-01 07:00:00 +0000
Date found: 1994-11-01 07:00:00 +0000
Date found: 1994-10-01 07:00:00 +0000
Date found: 1994-09-01 06:00:00 +0000
Date found: 1994-08-01 06:00:00 +0000
Date found: 1994-07-01 06:00:00 +0000
Date found: 1994-06-01 06:00:00 +0000
Date found: 1994-05-01 06:00:00 +0000
Date found: 1994-04-01 06:00:00 +0000
Date found: 1994-03-01 07:00:00 +0000
Date found: 1994-02-01 07:00:00 +0000
Date found: 1994-01-01 07:00:00 +0000
Date found: 1993-12-01 07:00:00 +0000
Date found: 1993-11-01 07:00:00 +0000
Date found: 1993-10-01 07:00:00 +0000
Date found: 1993-09-01 06:00:00 +0000
Date found: 1993-08-01 06:00:00 +0000
Date found: 1993-07-01 06:00:00 +0000
Date found: 1993-06-01 06:00:00 +0000
Date found: 1993-05-01 06:00:00 +0000
Date found: 1993-04-01 06:00:00 +0000
Date found: 1993-03-01 07:00:00 +0000
Date found: 1993-02-01 07:00:00 +0000
Date found: 1993-01-01 07:00:00 +0000
Date found: 1992-12-01 07:00:00 +0000
Date found: 1992-11-01 07:00:00 +0000
Date found: 1992-10-01 07:00:00 +0000
Date found: 1992-09-01 06:00:00 +0000
Date found: 1992-08-01 06:00:00 +0000
Date found: 1992-07-01 06:00:00 +0000
Date found: 1992-06-01 06:00:00 +0000
Date found: 1992-05-01 06:00:00 +0000
Date found: 1992-04-01 06:00:00 +0000
Date found: 1992-03-01 07:00:00 +0000
Date found: 1992-02-01 07:00:00 +0000
Date found: 1992-01-01 07:00:00 +0000
Date found: 1991-12-01 07:00:00 +0000
Date found: 1991-11-01 07:00:00 +0000
Date found: 1991-10-01 07:00:00 +0000
Date found: 1991-09-01 06:00:00 +0000
Date found: 1991-08-01 06:00:00 +0000
Date found: 1991-07-01 06:00:00 +0000
Date found: 1991-06-01 06:00:00 +0000
Date found: 1991-05-01 06:00:00 +0000
Date found: 1991-04-01 06:00:00 +0000
Date found: 1991-03-01 07:00:00 +0000
Date found: 1991-02-01 07:00:00 +0000
Date found: 1991-01-01 07:00:00 +0000
Date found: 1990-12-01 07:00:00 +0000
Date found: 1990-11-01 07:00:00 +0000
Date found: 1990-10-01 07:00:00 +0000
Date found: 1990-09-01 06:00:00 +0000
Date found: 1990-08-01 06:00:00 +0000
Date found: 1990-07-01 06:00:00 +0000
Date found: 1990-06-01 06:00:00 +0000
Date found: 1990-05-01 06:00:00 +0000
Date found: 1990-04-01 06:00:00 +0000
Date found: 1990-03-01 07:00:00 +0000
Date found: 1990-02-01 07:00:00 +0000
Date found: 1990-01-01 07:00:00 +0000
Date found: 1989-12-01 07:00:00 +0000
Date found: 1989-11-01 07:00:00 +0000
Date found: 1989-10-01 07:00:00 +0000
Date found: 1989-09-01 06:00:00 +0000
Date found: 1989-08-01 06:00:00 +0000
Date found: 1989-07-01 06:00:00 +0000
Date found: 1989-06-01 06:00:00 +0000
Date found: 1989-05-01 06:00:00 +0000
Date found: 1989-04-01 06:00:00 +0000
Date found: 1989-03-01 07:00:00 +0000
Date found: 1989-02-01 07:00:00 +0000
Date found: 1989-01-01 07:00:00 +0000
Date found: 1988-12-01 07:00:00 +0000
Date found: 1988-11-01 07:00:00 +0000
Date found: 1988-10-01 07:00:00 +0000
Date found: 1988-09-01 06:00:00 +0000
Date found: 1988-08-01 06:00:00 +0000
Date found: 1988-07-01 06:00:00 +0000
Date found: 1988-06-01 06:00:00 +0000
Date found: 1988-05-01 06:00:00 +0000
Date found: 1988-04-01 06:00:00 +0000
Date found: 1988-03-01 07:00:00 +0000
Date found: 1988-02-01 07:00:00 +0000
Date found: 1988-01-01 07:00:00 +0000
Date found: 1987-12-01 07:00:00 +0000
Date found: 1987-11-01 07:00:00 +0000
Date found: 1987-10-01 07:00:00 +0000
Date found: 1987-09-01 06:00:00 +0000
Date found: 1987-08-01 06:00:00 +0000
Date found: 1987-07-01 06:00:00 +0000
Date found: 1987-06-01 06:00:00 +0000
Date found: 1987-05-01 06:00:00 +0000
Date found: 1987-04-01 06:00:00 +0000
Date found: 1987-03-01 07:00:00 +0000
Date found: 1987-02-01 07:00:00 +0000
Date found: 1987-01-01 07:00:00 +0000
Date found: 1986-12-01 07:00:00 +0000
Date found: 1986-11-01 07:00:00 +0000
Date found: 1986-10-01 07:00:00 +0000
Date found: 1986-09-01 06:00:00 +0000
Date found: 1986-08-01 06:00:00 +0000
Date found: 1986-07-01 06:00:00 +0000
Date found: 1986-06-01 06:00:00 +0000
Date found: 1986-05-01 06:00:00 +0000
Date found: 1986-04-01 06:00:00 +0000
Date found: 1986-03-01 07:00:00 +0000
Date found: 1986-02-01 07:00:00 +0000
Date found: 1986-01-01 07:00:00 +0000
Date found: 1985-12-01 07:00:00 +0000
Date found: 1985-11-01 07:00:00 +0000
Date found: 1985-10-01 07:00:00 +0000
Date found: 1985-09-01 06:00:00 +0000
Date found: 1985-08-01 06:00:00 +0000
Date found: 1985-07-01 06:00:00 +0000
Date found: 1985-06-01 06:00:00 +0000
Date found: 1985-05-01 06:00:00 +0000
Date found: 1985-04-01 06:00:00 +0000
Date found: 1985-03-01 07:00:00 +0000
Date found: 1985-02-01 07:00:00 +0000
Date found: 1985-01-01 07:00:00 +0000
Date found: 1984-12-01 07:00:00 +0000
Date found: 1984-11-01 07:00:00 +0000
Date found: 1984-10-01 07:00:00 +0000
Date found: 1984-09-01 06:00:00 +0000
Date found: 1984-08-01 06:00:00 +0000
Date found: 1984-07-01 06:00:00 +0000
Date found: 1984-06-01 06:00:00 +0000
Date found: 1984-05-01 06:00:00 +0000
Date found: 1984-04-01 06:00:00 +0000
Date found: 1984-03-01 07:00:00 +0000
Date found: 1984-02-01 07:00:00 +0000
Date found: 1984-01-01 07:00:00 +0000
Date found: 1983-12-01 07:00:00 +0000
Date found: 1983-11-01 07:00:00 +0000
Date found: 1983-10-01 07:00:00 +0000
Date found: 1983-09-01 06:00:00 +0000
Date found: 1983-08-01 06:00:00 +0000
Date found: 1983-07-01 06:00:00 +0000
Date found: 1983-06-01 06:00:00 +0000
Date found: 1983-05-01 06:00:00 +0000
Date found: 1983-04-01 06:00:00 +0000
Date found: 1983-03-01 07:00:00 +0000
Date found: 1983-02-01 07:00:00 +0000
Date found: 1983-01-01 07:00:00 +0000
Date found: 1982-12-01 07:00:00 +0000
Date found: 1982-11-01 07:00:00 +0000
Date found: 1982-10-01 07:00:00 +0000
Date found: 1982-09-01 06:00:00 +0000
Date found: 1982-08-01 06:00:00 +0000
Date found: 1982-07-01 06:00:00 +0000
Date found: 1982-06-01 06:00:00 +0000
Date found: 1982-05-01 06:00:00 +0000
Date found: 1982-04-01 06:00:00 +0000
Date found: 1982-03-01 07:00:00 +0000
Date found: 1982-02-01 07:00:00 +0000
Date found: 1982-01-01 07:00:00 +0000
Date found: 1981-12-01 07:00:00 +0000
Date found: 1981-11-01 07:00:00 +0000
Date found: 1981-10-01 07:00:00 +0000
Date found: 1981-09-01 06:00:00 +0000
Date found: 1981-08-01 06:00:00 +0000
Date found: 1981-07-01 06:00:00 +0000
Date found: 1981-06-01 06:00:00 +0000
Date found: 1981-05-01 06:00:00 +0000
Date found: 1981-04-01 06:00:00 +0000
Date found: 1981-03-01 07:00:00 +0000
Date found: 1981-02-01 07:00:00 +0000
Date found: 1981-01-01 07:00:00 +0000
Date found: 1980-12-01 07:00:00 +0000
Date found: 1980-11-01 07:00:00 +0000
Date found: 1980-10-01 07:00:00 +0000
Date found: 1980-09-01 06:00:00 +0000
Date found: 1980-08-01 06:00:00 +0000
Date found: 1980-07-01 06:00:00 +0000
Date found: 1980-06-01 06:00:00 +0000
Date found: 1980-05-01 06:00:00 +0000
Date found: 1976-04-01 07:00:00 +0000

2020-01-01 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 177 174 111
2020-01-02 482 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 177 174 111
2020-01-03 482 482 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 177 174 111
2020-01-04 482 482 482 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 177 174 111
2020-01-05 482 482 482 482 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 189 177 174 111
...
2020-01-27 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 189 189 177 174 111
2020-01-28 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 189 177 174 111
2020-01-29 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 201 177 174 111
2020-01-30 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 201 189 174 111
2020-01-31 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 482 201 189 174 111