title: Protocol referencing another protocol via a property crash SourceKitService and Playground
body: <p>I'm experimenting with protocols and delegates and figured this should be possible:</p>
  
  <pre><code>protocol MyProtocolDelegate {
      func myProtocolDidThat(myProtocol: MyProtocol)
  }
  
  protocol MyProtocol {
      var delegate: MyProtocolDelegate? { get set }
  }
  </code></pre>
  
  <p>However, the SourceKitService will crash again and again if I use the above code in Playground or a project. If I compile it gives:</p>
  
  <pre><code>Swift Compiler Error - Command failed due to signal: Segmentation fault: 11
  </code></pre>
  
  <p>If I change <code>MyProtocol</code> to  a class everything works fine. Is this is Swift bug or a deliberate restriction? Looking at Swift with a Java background, where interfaces referencing interfaces isn't unusual, I'm a bit puzzled that this happens with Swift.</p>
  
  <p>I'm using Xcode 6.0.1.</p>