TempDir.scala

import sbt.Keys._
import sbt._

import java.nio.file.Files

object TempDir extends AutoPlugin {
  object autoImport {
    lazy val tempDir = taskKey[File]("Sets target.temp.directory Java property. Creates the directory if needed.")
  }
  import autoImport._

  val tempDirSetting = tempDir := {
    val file = target.value / "tmp"
    Files.createDirectories(file.toPath)
    // The following is SHARED between all non-forked tests, which makes the actual
    // value used by a test non-deterministic when running root/test or root/it:test
    System.setProperty("target.temp.directory", file.getAbsolutePath)
    file
  }

  override def projectSettings = Seq(
    tempDirSetting,
    test in Test <<= (test in Test) dependsOn tempDir,
    javaOptions in Test += s"-Dtarget.temp.directory=${tempDir.value}"
  )
}