Unhardcode default JVM args

[retronym]

e.g. -XX:MaxPermSize=640M.

I'm trying to set up a Java 9 community build and this option now is unavailable. (In Java 8, it is a no op but allowed.)

[retronym]

object SbtRunner {
  // TODO - Configure these somewhere?
  val defaultJavaArgs = Seq(
    "-XX:+CMSClassUnloadingEnabled",
    "-XX:+DoEscapeAnalysis",
    "-Xms1536m",
    "-Xmx1536m",
    "-Xss2m",
    "-XX:MaxPermSize=640m",
    "-XX:ReservedCodeCacheSize=192m"
  )

[gkossakowski]

:+1:

I can't think of any workaround. @cunei, are those settings needed at all? Problems with permgen and code caches were addressed in sbt itself, right?

[cunei]

Those settings are useful, in the sense that they are defaults that allow stuff like the community build to work even if the user has no special java options defined. However, I agree that there should be a way to override them. I will add a further configuration option.