Add Scala 2 version of case classes that can evolve

[julienrf]

The same approach as with Scala 3 also works with Scala 2 if you add the -Xsource:3 compiler option.

[sideeffffect]

Just to be clear, with -Xsource:3 and case class constructor private, both copy (in class) and apply (in companion) are private too?

[julienrf]

Just to be clear, with -Xsource:3 and case class constructor private, both copy (in class) and apply (in companion) are private too?

Yes.

[sideeffffect]

But to be super duper clear, that means that adding -Xsource:3 is a breaking change (assuming the project in question is using case classes), right?

[julienrf]

Indeed.