Xcode 11 iOS 12 crash: failed to demangle witness for associated type

AppDelegate.swift

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
  var window: UIWindow?

  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    print(process(MyFoo()))
    return true
  }
}

struct MyFoo: Foo {
  var body: some Foo {
    return Bar()
  }
}

public func process<Out: Foo>(_ foo: Out) -> String {
  print("hi")
  return process(foo.body)
}

public protocol Foo {
  associatedtype Body: Foo
  var body: Body { get }
}

extension Never: Foo {
  public var body: Never {
    fatalError()
  }
}

struct Bar: Foo {
  typealias Body = Never

  public var body: Self.Body {
    fatalError()
  }
}