Case class with protected constructor has a public apply

[dwijnand]

Compiler version

3.1.0

Minimized code

sealed case class Foo protected (i: Int, j: Int)

final class Bar(n: Int) extends Foo(n, n)

class Other:
  def foo  = Foo(1, 2)
  def foo2 = Foo.apply(1, 2)

Output

$ scalac -3.1.0 foo.scala
$

Expectation

I shouldn't be able to construct a case class with a protected constructor in an Other class.

Notes

Looks like this was changed in #5830. I'd argue a protected constructor should mean everything a private one means with the addition that it can have subclasses because they can access the constructor. Meaning it shouldn't have an apply method (because it makes no sense in an object and may even will impact overload resolution) and therefore it shouldn't mixin its FunctionX either.

[dwijnand]

For a real world case, I was playing around with removing RealTypeBounds by making TypeBounds non-abstract but with a protected constructor so AliasingBounds can still extend it. But the current implementation made TypeBounds' synthetic apply (which doesn't use unique) publicly accessible.

[joroKr21]

Isn't it too late to change that? I.e. wouldn't it be binary incompatible? On the other hand if I'm not mistaken Scala 2.13 applies the same modifiers to apply and copy as well. If I said private I didn't mean to allow sneaky developers to work around my validations by using apply or copy.

[SethTisue]

if I'm not mistaken Scala 2.13 applies the same modifiers to apply and copy as well

yes, but only under -Xsource:3: scala/scala#7702

[joroKr21]

yes, but only under -Xsource:3: scala/scala#7702

I'm sure there's a joke somewhere there about predicting the future 😄