Open Radar

 
Summary:
When a protocol is defined with a static function that returns an optional self (`Optional<Self>`) and is implemented by a `final` class, SourceKit will crash when trying to call that method and assign it's return value to a variable.

Steps to Reproduce:
1. Open radar.playground
2. See SourceKit crash almost immediately

Expected Results:
SourceKit would not crash but be able to interpret code.

Actual Results:
SourceKit crashes.

Version:
- OS X 10.11.6 (15G1004)
- Xcode 7.3.1 (7D1014)
- Swift 2.2

Notes:


Configuration:
This will occur in both Swift Playgrounds as well as an Xcode project when implementing the same pattern as in the example playground.

----------------------------------------------------------------------
// radar.playground

import UIKit

protocol Foo {
    var name: String { get }
    static func fooObject() -> Optional<Self>
//    static func fooObject() -> Self? // works
}

final class Kung: Foo {
    var name = "Kung"
    static func fooObject() -> Kung? {
        return Kung()
    }
}

final class Bar: Foo {
    var name = "Bar"
    static func fooObject() -> Bar? {
        return Bar()
    }
}

// a helper function for one of the work arounds
func getInstance(forType type: Foo.Type) -> Foo? {
    return type.fooObject()
}

// works
//func printName(forType type: Foo.Type) {
//    let instance = getInstance(forType: type)
//    print(instance?.name)
//}

// works
//func printName(forType type: Foo.Type) {
//    print(type.fooObject()?.name)
//}

// doesn't work
func printName(forType type: Foo.Type) {
    let fooObject = type.fooObject() // crashes on this line
    print(fooObject?.name)
}

printName(forType: Kung.self)
printName(forType: Bar.self)