IntelliJ cannot resolve symbol in build.sbt

Question

IntelliJ IDEA 15 is reporting an unresolved symbol for my project definition in my build.sbt file

lazy val root = (project in file(".")).enablePlugins(PlayScala)

It's reporting an error with project and in.

Cannot resolve symbol project.
Cannot resolve symbol in.

Everything else resolves perfectly and the project is otherwise all set up, sbt builds fine, activator runs fine.

Answer 1

In my case, after upgrading Intellij forgot that the project was a Scala project.

Delete .idea/ and import the project to fix this.