vals in a nested singleton object may be initialized to null

Compiler version

3.0.0, 3.1.3, 3.2.0 and 3.2.2-RC1-bin-20221006-a6a3385-NIGHTLY

Minimized code

final case class Foo(name: String)

object Foo {
  object Foos {
    val Name1 = Foo("Apple")
    val Name2 = Foo("Banana")
    val Name3 = Foo("Cherry")
    // Using explicit `new`s prevents the issue
    // val Name1 = new Foo("Apple")
    // val Name2 = new Foo("Banana")
    // val Name3 = new Foo("Cherry")
  }

  val allFoos: Seq[Foo] = {
    import Foos._
    Seq(Name1, Name2, Name3)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    println(Foo.Foos.Name1)
    println(Foo.allFoos)
    // Accessing in the reverse order (or not accessing Name1 at all) prevents the issue
    // println(Foo.allFoos)
    // println(Foo.Foos.Name1)
  }
}

Output

Foo(Apple)
List(null, null, null)

Expectation

The output should be:

Foo(Apple)
List(Foo(Apple), Foo(Banana), Foo(Cherry))

Replacing any of the commented part of the program above prevents the issue. Also, Scala 2.13.9 produces the expected output without any modification. So, this is a behavior change between 2.13 and 3.

[liufengyun]

Related: #11262 #9176

Currently -Ysafe-init is not capable of handling static objects.

[som-snytt]

Sample Scala 2 issue

https://github.com/scala/bug/issues/3342