Xcode 9: lost syntax highlighting and autocomplete?

Have you ever been working on a project, and then one day your syntax highlighting is gone? Your autocomplete is generating almost nothing useful? This trick saved me from bouts of madness.

1. Quit Xcode
2. Finder > Go (hold down the Option key while Go is selected – this will cause Library to pop up)
3. Select Library
4. Developer > Xcode > Derived Data
5. Find the folder that has your app name & a jumble of characters behind it, i.e. “MyApp-dfwdfdfakjakjaka”
6. Delete the folder.
7. Launch Xcode and open your project
8. It will be re-indexed and you’ll see a folder pop back into your Derived Data folder for the project.
9. You should be good to go.