[swift-users] Linux - Calendar date(byAdding:to:wrappingComponents:) returns nil when it shouldn't?

Alex Blewitt alblue at apple.com
Wed Oct 5 11:23:35 CDT 2016

> On 5 Oct 2016, at 16:48, Alex Blewitt via swift-users <swift-users at swift.org> wrote:
>> On 4 Oct 2016, at 20:10, Jason Ji via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> Hello,
>> I'm having an issue with (NS)Calendar on Linux which I think is a bug, but I just wanted to check first if it was just me or if this is indeed a bug. I've filed a bug report here, just in case: https://bugs.swift.org/browse/SR-2846 <https://bugs.swift.org/browse/SR-2846>
>> In short, Calendar has a method date(byAdding:to:wrappingComponents:) which returns a new date which is the result of date arithmetic on the passed-in date. It works fine on El Capitan, but doesn't seem to work properly on Ubuntu 14.04. Below is some sample code:
>> import Foundation
>> let today = Date()
>> let diffComponents = DateComponents(day: -1)
>> let newDate = Calendar.current.date(byAdding: diffComponents, to: today)		//returns nil
>> I've tried this in the swift REPL on Ubuntu 14.04 with both Swift 3.0-RELEASE, and the latest snapshot (October 2).
>> If anyone else could try this out as a sanity check for me, that would be great - I'd be happy to be embarrassed that I've done something wrong.
> It's worth explicitly specifying a calendar (so that it rules out any environmental setup) -- for example, Calendar(identifier:.gregorian). However, I see 'nil' as well as the return result for this operation, so it could be a bug.

I think the bug is here:

https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/NSCalendar.swift#L464 <https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/NSCalendar.swift#L464>

        _convert(comps.isLeapMonth, type: "L", vector: &vector, compDesc: &compDesc)

The leap month is defined with a capital letter here, but a lower-case letter when it's decoded:

https://github.com/apple/swift-corelibs-foundation/blob/338f4bf3a89c75a0420b49f5701466e106af02b5/CoreFoundation/Locale.subproj/CFCalendar.c#L423 <https://github.com/apple/swift-corelibs-foundation/blob/338f4bf3a89c75a0420b49f5701466e106af02b5/CoreFoundation/Locale.subproj/CFCalendar.c#L423>

    case 'l': return UCAL_IS_LEAP_MONTH;

The lower-case l should be the correct version so this probably needs to be changed here. In addition, there are optional-of-bool issues here; the 'comps.isLeapMonth' is a boolean value, which means it attempts to roll forward the leap month (which doesn't make sense). I think the error was introduced here, although it didn't help that the capitalisation was also wrong at the time:

https://github.com/apple/swift-corelibs-foundation/commit/d3300b7118924d6ad8ba411d317f33eade854bc5 <https://github.com/apple/swift-corelibs-foundation/commit/d3300b7118924d6ad8ba411d317f33eade854bc5> 


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