"Private" primary constructor vs MiMa

julienrf · January 13, 2023, 8:22am

After more discussion, we concluded that this should be handled at the MiMa level, so I have created that issue:

Private class constructors should be ignored

opened 08:17AM - 13 Jan 23 UTC

MiMa flags changes in private constructor signatures: ~~~ scala // v1.scala … case class Person private (name: String) object Person: def apply(name: String): Person = new Person(name) ~~~ ~~~ scala // v2.scala case class Person private (name: String, address: Option[String]) object Person: def apply(name: String): Person = new Person(name, None) def apply(name: String, address: String): Person = new Person(name, Some(address)) ~~~ Here, MiMa fails with a message like: > method this(java.lang.String)Unit in class Person does not have a correspondent in current version However, the constructor is private, so the change is safe. What happens is that although the constructor can’t be called from Scala code, it is effectively public in the bytecode (just like `private[x]` members). MiMa should detect this pattern and ignore the changes to private class constructors. Related discussions: https://github.com/scala/bug/issues/12711 https://github.com/lampepfl/dotty/issues/16651 https://github.com/scala/docs.scala-lang/pull/2662 https://contributors.scala-lang.org/t/private-primary-constructor-vs-mima/6050 PR ignoring `private[x]` members: https://github.com/lightbend/mima/pull/583