Open Radar

 
Area:
Foundation

Summary:
In certain setups (see example) Calendar.enumerateDates produces unexpected results that differ from the iOS 10 implementation. 

Steps to Reproduce:
Run the following code

import Foundation

let date = Date(timeIntervalSinceReferenceDate: 525913200)
let calendar = Calendar.current

let components = calendar.dateComponents([.month, .hour], from: date)
var dates = [Date]()

var count = 0
calendar.enumerateDates(startingAfter: date, matching: components, matchingPolicy: .strict) { (date, exact, stop) in
    
    print(date ?? "nil")
    count += 1
    stop = count > 5
}

Expected Results:
Print dates incremented by day (that's what happens in iOS 10):

2017-09-01 23:00:00 +0000
2017-09-02 23:00:00 +0000
2017-09-03 23:00:00 +0000
2017-09-04 23:00:00 +0000
2017-09-05 23:00:00 +0000
2017-09-06 23:00:00 +0000

Actual Results:
Dates are incremented by year:

2018-08-31 23:00:00 +0000
2019-08-31 23:00:00 +0000
2020-08-31 23:00:00 +0000
2021-08-31 23:00:00 +0000
2022-08-31 23:00:00 +0000
2023-08-31 23:00:00 +0000

Version/Build:
iOS 11 beta from Xcode Version 9.0 beta 6 (9M214v) 
Also seen in the attached playground.