title: Migration to Swift 4 from Swift 3.2 giving "failed to import bridging header " error
body: <p>As apple has released Xcode 9 beta version with Swift 4.0 support. I have been trying to upgrade my code to Swift 4.0 from Swift 3.2. But it keeps giving me <code>failed to import bridging header</code> error whereas my project build successfully.</p>
  <p>Xcode error detail:</p>
  <blockquote>
  <p><strong>Convert to Current Swift Syntax Failed</strong></p>
  <p>Please ensure that all selected targets build successfully with the currently configured Swift version before attempting a migration.</p>
  </blockquote>
  <p>Has anybody faced the similar error while upgrading code base to swift 4.</p>