Is this a language bug or expected behaviour when nesting classes inside methods?

Question
1

I am getting an unusual stack overflow exception which may be a language bug. The issue arrises when I nest a class and its companion object inside a method.
The following (pointless) code prints “Done!” without a problem:

    object Foo extends App {
      final case class Person(name: String)
      object Person {
    val me = Person("Cameron")
      }
      val _ = Person.me
      println("Done!")
    }

However if I nest some of it in a method the code still compiles, but throws an exception:

 object Foo extends App {
          def method(): Unit = {
            final case class Person(name: String)
            object Person {
              val me = Person("Cameron")
            }
            val _ = Person.me
          }
          method()
          println("Done!")
        }

I used Scala 2.13 to try this out, but first noticed the bug when using 2.12.
Could someone tell me if this is expected behaviour? It seems like it could be a language bug to me?

1 Like
2

Yes that looks like a bug to me.
If me is a lazy val or a def it doesn’t crash by the way. Or if Person is not a case class, or if you do new Person("Cameron") instead of calling the generated apply method.

3

Thanks, interesting how it only happens for val and not lazy val or def.
If this is a language bug what is the best way of reporting it? Should I post the same question in scala contributors?

4

Scala 2 bugs can be reported in Issues · scala/bug · GitHub. This behavior seems to exist in Scala 3 as well, so perhaps you could open an issue there too (Issues · lampepfl/dotty · GitHub) and reference the Scala 2 issue.

5

Thank you for your help - I’ve raised an issue for both Scala 2 (Stack overflow error when nesting a case class and its companion object inside a method · Issue #12435 · scala/bug · GitHub) and Scala 3 (Stack overflow error when nesting a case class and its companion object inside a method · Issue #13162 · lampepfl/dotty · GitHub)

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