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Here is a quick experiment to demonstrate an inconsistent behaviour:

trait Foundation {

  import Foundation.*

  {
    initialisationCounter.incrementAndGet()
  }

  case class Top1() {
  }
}

object Foundation {

  lazy val initialisationCounter = new AtomicInteger()
}

(in 2 different packages pkg1 & pkg2)

package object pkg1 extends Foundation {}

package object pkg2 {

  {
    initialisationCounter.incrementAndGet()
  }

  case class Top1() {}
}

(in a Scalatest suite)


class PackageObjInit extends SparkEnvSpec {

  it("for package object inheriting a trait") {

    Foundation.initialisationCounter.set(0)

    val top = pkg1.Top1()
    assert(Foundation.initialisationCounter.intValue() == 1)
  }

  it("for self-contained package object") {

    Foundation.initialisationCounter.set(0)

    val top = pkg2.Top1()
    assert(Foundation.initialisationCounter.intValue() == 1)
  }
}

I expect the construction of both package objects to behave consistently, namely they should both be constructed on first import or first use of the case class that depends on them. Instead. Only the first test case succeeded.

Is it a design flaw of the compiler or a deliberate implementation intend to circumvent some self-referencing soundness hole? How can I determine the right moment of construction in other cases?

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