@import Foundation;
@interface Base<Element>: NSObject
- (nonnull id)objectForKeyedSubscript:(nonnull Element)key;
@end

// compile with "-import-objc-header objc.h"
class Sub: Base<NSObject> {
  override subscript(key: NSObject) -> Any { return self }
}

test.swift:2:12: error: subscript does not override any subscript from its superclass
  override subscript(key: NSObject) -> Any { return self }
           ^
__ObjC.Base:3:10: note: potential overridden subscript 'subscript' here
    open subscript(key: Element) -> Any { get }
         ^