Open Radar

 
Area:
UserNotifications Framework

Summary:
UNCalendarNotificationTrigger does not give accurate `next trigger date` calculations.

Steps to Reproduce:
0.
let us say that our current month is June (someday before 30).

1. TriggerDate in UNCalendarNotificationTrigger
let components = DateComponents(day: 31)
let trigger = UNCalendarNotificationTrigger(dateMatching: target, repeats: true)
print(trigger.nextTriggerDate())

2. NextDate in Date
let components = DateComponents(day: 31)
let next = Calendar.current.nextDate(after: Date(), matching: components, matchingPolicy: .nextTime, repeatedTimePolicy: .first, direction: .forward)
print(next)

3. Negative parameters in DateComponents
let components = DateComponents(day: 1, hour: -24)
let trigger = UNCalendarNotificationTrigger(dateMatching: target, repeats: true)
print(trigger.nextTriggerDate())

Expected Results:
1. Jul 31, 2017, 12:00 AM //since there is no '31' in June.
2. Jul 31, 2017, 12:00 AM //since there is no '31' in June.
3. Jun 30, 2017, 12:00 AM //since it's the last day of June.

Observed Results:
1. Jul 1, 2017, 12:00 AM
2. Jul 1, 2017, 12:00 AM
3. nil

Notes:
For #3,
Traditional date calculation method successfully calculates negative values as follows:

let components = DateComponents(year: 2017, month: 7, day: 1, hour: -24)
let date = Calendar.current.date(from: components)!  // gives: Jun 30, 2017, 12:00 AM

, but not in new iOS10 methods.