Issue Description:

Marking a protocol with @objc will trick the compiler into thinking that using .self will yield an AnyClass type. The runtime through will determine otherwise and the usage will cause a crash.

i.e.

@objc protocol X {

var answerToEverything: Int { get }

{{}}}

let bundle = Bundle(for: X.self) -> ``Thread 1: EXC_BAD_ACCESS (code=1,..)

Removing the @objc, however, will result in the following compiler error:

Cannot convert value of type 'X.Protocol' to expected argument type 'AnyClass' (aka 'AnyObject.Type')

which actually gives us a hint into the problem: we're supposed to pass in AnyClass, not protocols, structs, enums or any other types.

I can't begin to assume how this should be fixed: by either not allowing the @objc protocol usage at compile time or by extending the API to allow protocols, structs, enums Types, but I am more than happy to listen to other opinions on this matter. Maybe this is more a feature than a bug.

Observation: making the non @objc protocol conform to either the deprecated class or AnyObject still does not make the compiler allow the usage.