Swift 4.0 Eventkit Cannot get calendars and events correctly

Question

I'm trying to use Eventkit to access Mac Calendar. Access is successfully requested but I keep getting nil or an empty array of calendar or events, even though I have several calendars and many eventsin local calendar, iCloud calendar, and Google calendar in the app.
The output I get from the following code is: On My Mac [] []

    let sources = eventStore.sources
    for source in sources{
        print(source.title)
        for calendar in source.calendars(for: .event){
            print(calendar.title)
        }
    }

    let calendars = eventStore.calendars(for: .event)
    let predicate = self.eventStore.predicateForEvents(withStart: startDate, end: endDate, calendars: nil)
    let events = self.eventStore.events(matching: predicate)
    print(calendars)
    print(events)

And if I try to create and save a calendar from code, then I'm getting error: Error Domain=EKErrorDomain Code=5 "Attempted to save when persistence was unavailable" UserInfo={NSLocalizedDescription=Attempted to save when persistence was unavailable}

Answer 1

After lots of trial and error, I found the answer.

You need to set the com.apple.security.personal-information.calendars key to YES in your entitlements file, even if your app is not sandboxed. There is a bug in Apple's implementation of EventKit that prevents your app getting access to calendars if it does not set this key, even if the sandbox is disabled.