Private class constructors should be ignored

[julienrf]

MiMa flags changes in private constructor signatures:

// v1.scala
case class Person private (name: String)

object Person:
  def apply(name: String): Person = new Person(name)

// 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:

scala/bug#12711
scala/scala3#16651
scala/docs.scala-lang#2662
https://contributors.scala-lang.org/t/private-primary-constructor-vs-mima/6050

PR ignoring private[x] members: #583

[jeroentervoorde]

@SethTisue Could you take a look at my approach in #778 please?
Especially the bit on whether privateWithin constructors need to be ignored as well.

[julienrf]

The issue is fixed by #778.

[mr-git]

was this released? I couldn't find if "ch.epfl.scala" % "sbt-version-policy" % "3.2.1" includes the fix for this

[SethTisue]

#778 hasn't appeared in a release yet. Thanks for bringing it up; we're overdue for a release. I've opened a ticket on it and assigned myself: #816