title: Xcode 8.3 Core Data "use of undeclared type" error
body: <p>After updating to Xcode 8.3 (and subsequently 8.3.2) my app continues to build, however code completion has completely broken.</p>
  
  <p>From what I can tell, Xcode simply doesn't recognize my Core Data classes anymore, but for some reason, the build still completes successfully, and the app itself works as it did before. The consequence is that I have a ton of <code>use of undeclared type: [entity name]</code> errors, and code completion no longer works. </p>
  
  <p>Here's what I've tried in order to fix.</p>
  
  <ul>
  <li>Delete the Core Data model and reconfigure it, from scratch.</li>
  <li>Clean build folder</li>
  <li>Manually delete the DerivedData folder</li>
  <li>Close/reopen xcode</li>
  <li>Cry a little, but only on the inside</li>
  <li>Change Codegen setting from <code>Class Definition</code> to <code>Category/Extension</code>, build, then reset, while also doing cleans and manual DerivedData folder deletes in between</li>
  <li>Validate the Target is set correctly for the model file</li>
  <li>Add <code>import CoreData</code> to literally every file that contains a reference to a model class</li>
  <li>Create dummy classes of the entities, which breaks the build and the original <code>undeclared</code> errors are replaced with <code>invalid redeclaration of [entity name]</code>.</li>
  <li>Update all entities <code>Module</code> setting to <code>Current Product Module</code></li>
  <li>Clean project, clean build folder, delete derived data folder, restart xcode, build, in that order.</li>
  </ul>
  
  <p>I'm convinced this is a bug with Xcode, but I'm hoping there's a way to resolve this without waiting for apple.</p>