java.lang.NoClassDefFoundError: cats/free/Inject$ building master

[ml10]

I was going to see if I could debug why the Applicative composition exercise doesn't display correctly and in trying to build exercises-cats, I ran into the NoClassDefFoundError above.

I checked on another computer and then tried the hseeberger/scala-sbt docker image to make sure I was starting clean. I got the same result all three times.

Steps to reproduce with hseeberger/scala-sbt docker image:

1. sudo docker run -it --rm hseeberger/scala-sbt
2. git clone https://github.com/scala-exercises/exercises-cats.git
3. cd exercises-cats/
4. sbt compile publishLocal

These steps should yield this stack trace:

java.lang.NoClassDefFoundError: cats/free/Inject$
	at github4s.Github.repos$lzycompute(Github.scala:40)
	at github4s.Github.repos(Github.scala:40)
	at org.scalaexercises.compiler.Compiler.org$scalaexercises$compiler$Compiler$$fetchContributions$1(Compiler.scala:163)

As a quick attempt to fix this, I added cats-free to the build.sbt file, and this yielded another stack trace.

java.lang.NoSuchMethodError: cats.free.Free.foldMap(Lcats/arrow/FunctionK;Lcats/Monad;)Ljava/lang/Object;
	at github4s.Github$GithubIOSyntaxEither.execK(Github.scala:58)
	at github4s.Github$GithubIOSyntaxEither.exec(Github.scala:64)
	at org.scalaexercises.compiler.Compiler.org$scalaexercises$compiler$Compiler$$fetchContributions$1(Compiler.scala:167)

It looks like I need another version of cats-free, but I'm not sure which one.