title: Convert to Current Swift Syntax Failed - "No such module" (Swift 4, Xcode 9)
body: <p>In Xcode 9, I am trying to do the automatic conversion to Swift 4.
  It fails with the following message:</p>
  
  <p><a href="https://i.stack.imgur.com/6Gu7C.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6Gu7C.png" alt="enter image description here"></a></p>
  
  <blockquote>
    <p><strong>Convert to Current Swift Syntax Failed</strong><br>
    Please ensure that all selected targets build successfully with the currently configured Swift version before attempting a migration.</p>
  </blockquote>
  
  <p>It's complaining of a missing module. But when I do a regular build there are no issues. Not sure if this is relevant, but the module (which Xcode is complaining is missing) was already converted to Swift 4 earlier (in it's own project).</p>
  
  <p>Note: No Cocoapods / Carthage used here.</p>
  
  <p>Note: Two solutions tried (and worked) but do not address the underlying issue.</p>
  
  <ul>
  <li>One solution is to do the conversion manually (change Swift version to 4 in build setting and apply Fix-Its one by one until no more build errors).</li>
  <li>Another solution is to disable the third party framework (comment out all code where it's used), do the auto-migration, and then re-enable the framework. This could get pretty difficult with bigger projects.</li>
  </ul>