SBT project refresh failed [IntelliJ, Scala, SBT]

Question

Whenever I try to enable auto-import in IntelliJ it always gives me this error:

SBT 'Example' project refresh failed

Error while importing SBT project:
...
[warn] ==== public: tried
[warn]   https://repo1.maven.org/maven2/org/scalatest/scalatest_2.12/2.2.6/scalatest_2.12-2.2.6.pom
[info] Resolving org.scala-lang#scala-compiler;2.12.0 ...
[info] Resolving org.scala-lang#scala-reflect;2.12.0 ...
[info] Resolving org.scala-lang.modules#scala-xml_2.12;1.0.5 ...
[info] Resolving jline#jline;2.14.1 ...
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  ::          UNRESOLVED DEPENDENCIES         ::
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  :: org.scalatest#scalatest_2.12;2.2.6: not found
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn] 
[warn]  Note: Unresolved dependencies path:
[warn]      org.scalatest:scalatest_2.12:2.2.6 (/Users/sarahbaka/Desktop/Scala/Example/build.sbt#L7-8)
[warn]        +- default:example_2.12:1.0
[trace] Stack trace suppressed: run 'last *:update' for the full output.
[trace] Stack trace suppressed: run 'last *:ssExtractDependencies' for the full output.
[error] (*:update) sbt.ResolveException: unresolved dependency: org.scalatest#scalatest_2.12;2.2.6: not found
[error] (*:ssExtractDependencies) sbt.ResolveException: unresolved dependency: org.scalatest#scalatest_2.12;2.2.6: not found
[error] Total time: 4 s, completed 08-Nov-2016 22:24:34</pre><br/>

I already installed the JetBrains Scala plugin, then opened a directory with an SBT build and reset/restarted my cache (File -> Invalidate Caches / Restart). But it still doesn't work! Does anyone know why?

Solution

Your scalatest dependency is misconfigured. You want scalatest version 2.6 published for Scala 2.12. There is no such combination, hence your build fails. If you have a look at which version of scalatest is available for Scala 2.12, here's the link. As you can see, it's only version 3.0.0. So, you have 3 options (those are changes in your build.sbt file you need to make):

1. Update your scalatest version to 3.0.0: libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.0" % Test
2. Downgrade your Scala version to 2.11: scalaVersion := "2.11.8"
3. Both of the above

I'd say it's a bit too early to use Scala 2.12, since it was only released a couple of days ago, and not all of the dependencies are published for it yet. Scala major versions (2.11 vs 2.12 is a major version upgrade for Scala) are not binary compatible, so you can't use a library compiled with one Scala version in a project that uses the other.

At the same time, I'd go with scalatest 3.0.0 version, since it's the stable one. So all in all, I'd go for option 3 at the moment, even though options 1 and 2 will fix this particular problem, in different ways.