Bug in swift 2.0 NSDateFormatter? [duplicate] - swift

Question

This question already has an answer here:
DateFormatter's returns nil for specific date strings without time in Swift
(1 answer)
Closed 7 years ago.
NSDateFormatter doesn't seem to like October Eighteenth. Tried every other date with success. (???)
It is almost certainly a bug in swift 2.0 (and if it is what should I do? I need to submit my app really soon). Am I missing something?
Checked it in playground on Xcode 7.0.1:
let str = "2015-10-18"
let str2 = "2015-10-14"
let formatter = NSDateFormatter()
formatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
formatter.dateFormat = "yyyy-MM-dd"
var date = formatter.dateFromString(str)
var date2 = formatter.dateFromString(str2)
Output:
"2015-10-18"
"2015-10-14"
<NSDateFormatter: 0x7f8aa050b760>
<NSDateFormatter: 0x7f8aa050b760>
<NSDateFormatter: 0x7f8aa050b760>
nil
"Oct 14, 2015, 12:00 AM"

Answer 1

The behavior depends on which timeZone the formatter using.
For example: America/Sao_Paulo
In Sao Paulo, http://www.timeanddate.com/time/change/brazil/sao-paulo?year=2015
Sunday, 18 October 2015, 00:00:00 clocks are turned forward 1 hour to
Sunday, 18 October 2015, 01:00:00 local daylight time instead
That means, there is no 2015-10-18 00:00:00 in Sao Paulo.
And as for NSDateFormatter, when it receives no time information from string, it assumes the time is 00:00:00 in its timezone. That's why it returns nil.
let formatter = NSDateFormatter()
formatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
formatter.timeZone = NSTimeZone(name: "America/Sao_Paulo")
formatter.dateFormat = "yyyy-MM-dd HH:mm"
formatter.dateFromString("2015-10-18 00:00") // -> nil
formatter.dateFromString("2015-10-18 00:30") // -> nil
formatter.dateFromString("2015-10-18 01:00") // -> non nil
As #LeoDabus stated, when you specify .calendar on the formatter:
it assumes the time is 00:00:00 in its timezone.
it will assume the start of the day for that date.
let formatter = NSDateFormatter()
formatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
formatter.timeZone = NSTimeZone(name: "America/Sao_Paulo")
formatter.dateFormat = "yyyy-MM-dd"
formatter.calendar = NSCalendar(identifier: NSCalendarIdentifierGregorian)
formatter.dateFromString("2015-10-17") // -> Oct 17, 2015, 12:00 AM
formatter.dateFromString("2015-10-18") // -> Oct 18, 2015, 1:00 AM
formatter.dateFromString("2015-10-19") // -> Oct 19, 2015, 12:00 AM