Open Radar

 
Summary:

Initializing a class from protocol associated type fails with "Use of unimplemented initializer".


Steps to Reproduce:

Create a macOS playground with the following code:

import Cocoa

protocol Component: class {
    static func createView() -> NSView
}

protocol GenericComponent: Component {
    associatedtype CoreClassAlias: NSView
}

class ParentView: NSView {
    
    init(custom: Int) {
        super.init(frame: .zero)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("Not implemented")
    }
}

class CustomView: ParentView {
    init() {
        super.init(custom: 0)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("Not implemented")
    }
}

class ConcreteComponent: Component, GenericComponent {
    typealias CoreClassAlias = CustomView
}

extension GenericComponent {
    static func createTypedView() -> CoreClassAlias {
        return CoreClassAlias.init()
    }
    
    static func createView() -> NSView {
        return createTypedView()
    }
}

var components: [Component.Type] = [
    ConcreteComponent.self
]

let generic = components[0]
let normalInitWorks = CustomView()
let thisDoesntWork = generic.createView()

Expected Results:
Either compiles and works, or doesn't compile and gives a reason.

Actual Results:
Compiles, doesn't work.
InitFailWithMetatype_macOS.playground: 11: 7: Fatal error: Use of unimplemented initializer 'init(frame:)' for class '__lldb_expr_48.ParentView'


Version/Build:
Swift 4.1, Xcode 9.3

Configuration:
Default