upgrade Scala 2.12.4 -> 2.12.6

[SethTisue]

I have no specific user-visible benefit in mind other than fewer
JARs to download for people who are on current versions of things

[dwijnand]

Uhhhh... lots and lots of these in CI:

[info] [error] java.lang.NullPointerException
[info] [error] 	at scala.collection.mutable.WrappedArray$ofRef.length(WrappedArray.scala:129)
[info] [error] 	at scala.collection.SeqLike.size(SeqLike.scala:105)
[info] [error] 	at scala.collection.SeqLike.size$(SeqLike.scala:105)
[info] [error] 	at scala.collection.AbstractSeq.size(Seq.scala:41)
[info] [error] 	at scala.collection.TraversableLike.$plus$plus(TraversableLike.scala:145)
[info] [error] 	at scala.collection.TraversableLike.$plus$plus$(TraversableLike.scala:143)
[info] [error] 	at scala.collection.mutable.ArrayOps$ofRef.$plus$plus(ArrayOps.scala:194)
[info] [error] 	at sbt.internal.Load$.defaultPreGlobal(Load.scala:85)
[info] [error] 	at sbt.internal.Load$.$anonfun$defaultLoad$1(Load.scala:63)
[info] [error] 	at sbt.internal.Load$.timed(Load.scala:1357)
[info] [error] 	at sbt.internal.Load$.defaultLoad(Load.scala:60)
[info] [error] 	at sbt.BuiltinCommands$.liftedTree1$1(Main.scala:744)
[info] [error] 	at sbt.BuiltinCommands$.doLoadProject(Main.scala:744)
[info] [error] 	at sbt.BuiltinCommands$.$anonfun$loadProjectImpl$2(Main.scala:715)
[info] [error] 	at sbt.Command$.$anonfun$applyEffect$4(Command.scala:142)
[info] [error] 	at sbt.Command$.$anonfun$applyEffect$2(Command.scala:137)
[info] [error] 	at sbt.Command$.process(Command.scala:181)
[info] [error] 	at sbt.MainLoop$.processCommand(MainLoop.scala:151)
[info] [error] 	at sbt.MainLoop$.$anonfun$next$2(MainLoop.scala:139)
[info] [error] 	at sbt.State$$anon$1.runCmd$1(State.scala:246)
[info] [error] 	at sbt.State$$anon$1.process(State.scala:250)
[info] [error] 	at sbt.MainLoop$.$anonfun$next$1(MainLoop.scala:139)
[info] [error] 	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:16)
[info] [error] 	at sbt.MainLoop$.next(MainLoop.scala:139)
[info] [error] 	at sbt.MainLoop$.run(MainLoop.scala:132)
[info] [error] 	at sbt.MainLoop$.$anonfun$runWithNewLog$1(MainLoop.scala:110)
[info] [error] 	at sbt.io.Using.apply(Using.scala:22)
[info] [error] 	at sbt.MainLoop$.runWithNewLog(MainLoop.scala:104)
[info] [error] 	at sbt.MainLoop$.runAndClearLast(MainLoop.scala:59)
[info] [error] 	at sbt.MainLoop$.runLoggedLoop(MainLoop.scala:44)
[info] [error] 	at sbt.MainLoop$.runLogged(MainLoop.scala:35)
[info] [error] 	at sbt.StandardMain$.runManaged(Main.scala:112)
[info] [error] 	at sbt.xMain.run(Main.scala:74)
[info] [error] 	at sbt.RunFromSourceMain$.launch(RunFromSourceMain.scala:39)
[info] [error] 	at sbt.RunFromSourceMain$.runImpl(RunFromSourceMain.scala:32)
[info] [error] 	at sbt.RunFromSourceMain$.run(RunFromSourceMain.scala:26)
[info] [error] 	at sbt.RunFromSourceMain$.main(RunFromSourceMain.scala:20)
[info] [error] 	at sbt.RunFromSourceMain.main(RunFromSourceMain.scala)
[info] [error] java.lang.NullPointerException

mayday, mayday?

[SethTisue]

maybe one of the 2.12.4's I changed to 2.12.6 actually needs to be 2.12.4 because it has to match the version of sbt that's building the code, something like that?

the NPE can come from:

scala> null: collection.mutable.WrappedArray[Int]
res8: scala.collection.mutable.WrappedArray[Int] = null

scala> res8.size
java.lang.NullPointerException

means there's some null coming from some indeterminate earlier point in time, looks hairy to investigate.

this PR was really more a reminder than something I intended to personally pursue, and the likelihood of this being caused by an actual regression in 2.12.5 or 2.12.6 seems fairly low to me.

[eed3si9n]

This is a bug of RunFromSourceMain.scala I think. See https://github.com/sbt/sbt/blob/1.x/sbt/src/test/scala/sbt/RunFromSourceMain.scala#L50-L56

  private def getConf(baseDir: File, args: Seq[String]): AppConfiguration = new AppConfiguration {
    def baseDirectory = baseDir
    def arguments = args.toArray
    def provider = new AppProvider { appProvider =>
      def bootDirectory: File = file(sys.props("user.home")) / ".sbt" / "boot"
      def scalaHome: File = bootDirectory / s"scala-$scalaVersion"
      def scalaProvider = new ScalaProvider { scalaProvider =>

the new scripted test uses sbtOn mechanism that no longer requires local publishing of sbt artifacts. It still needs to resolve the location of scala-compiler and scala-library JAR. It assumes that they are available in bootDirectory / s"scala-$scalaVersion". But this assumption does not hold when sbt doesn't yet use the patch release of Scala.
The workaround would be to manually resolve Scala using Ivy (like Launcher is doing internally) or call Launcher as a function.

[eed3si9n]

Closing this in favor of #4129