Answer by user363349 for Play framework tutorial: Cannot resolve symbol 'index'?

This process worked for me:

1. go into [File -> Project Structure -> Modules -> [YourAppModule] -> Sources Tab]
2. navigate to the "target/scala-[version]/src_managed" directory (panel on the right).
3. Right click the "main" directory and flag it as a source folder.
4. Right click "controllers" and "views" and remove the "sources" flag (you should see the controllers and views folder become package directories).
5. Apply -> OK -> recompile.

from https://github.com/playframework/playframework/issues/1784#issuecomment-26345523