Swift 3 / Xcode 8 Upgrade - 100's of DerivedData files missing from working copy errors

Question

I have just upgraded to the latest Beta version of XCode and Swift but after using the converter my app project now has over 200 build time yellow errors all stating /\"projectD

Answer 1

This is a bug in XCode. The missing files warnings disappear as soon as you git-commit your project tree.