I deleted the Objective-C files that Core Data generated from the data model, so I could go back to the swift files that I had generated in Xcode 7. When deleting the files, I had the files moved to the trash, and added the swift files back in to the project. I'm using Xcode 8.0.
The error I get is
"error: no such file or directory", for the missing files, one of which is Luna.build/DerivedSources/CoreDataGenerated/Luna/.LunaObservation+CoreDataClass.m. There are corresponding errors for LunaObservation+CoreDataProperties.m and LunaOrbit+CoreDataClass.m, but not LunaOrbit+CoreDataProperties.m.
I don't see the file's name in the build phase's compile sources. I've tried cleaning the project and deleting the derived data without success.
Update: I finally figured out how to generate Swift files instead of Objective-C files, but I'm still getting the error that it's looking for the deleted Objective-C files.
Update #2: I was able to reduce the number of errors after cleaning the project and deleting the entire derived data file; I no longer get errors for the missing .m and .h files, but I do get a single error about two missing files: .Orbit+CoreDataProperties.swift and .Observation+CoreDataProperties.swift. These files exist, but they don't have the period in front of the name. Attempting to add the period to the file name results in a "Rename failed" message. Both files had an extra "import" after the others that didn't import anything--the line just ended.
The post XCode 8 generates broken NSManagedObject subclasses for iOS 10 shows pretty much the problem I'm having.