Open Radar

 
When implementing an optional method of an ObjC protocol in an extension of a generic Swift class and annotating with @nonobjc, the compiler segfaults. 

If the optional protocol method is implemented in the class declaration and not the extension, no segfault occurs with or without the @nonobjc attribute.

If the method being implemented is not an optional method of an ObjC protocol, a compiler warning is provided "Non @objc method.....does not satisfy requirement of @objc protocol" along with "@objc is not supported with extensions of generic classes".

Steps to reproduce:

import Foundation
import CoreData

// Does not segfault

class Foo<T>: NSObject, NSFetchedResultsControllerDelegate {
    override init() {
        super.init()
    }
    
    @nonobjc func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    }
}

// Segfaults

class Bar<T>: NSObject {
    override init() {
        super.init()
    }
}

extension Bar: NSFetchedResultsControllerDelegate {
    @nonobjc func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    }
}


Expected Results:

Meaningful compiler error