constructor default parameters are reused for case class apply

[bishabosha]

A case class apply method does not have default parameters generated, instead the constructor default parameters are reused, I believe that this is undocumented - causing scala/bug#12409

Compiler version

3.0.1

Minimized code

case class CaseClassDefault(value: Int = 1)

val foo = Scala3CaseClass.apply()

Output

val foo: CaseClassDefault = CaseClassDefault.apply(CaseClassDefault.`<init>$default$1`)

Expectation

val foo: CaseClassDefault = CaseClassDefault.apply(CaseClassDefault.`apply$default$1`)

Notes

extract from generated code:

final lazy module val CaseClassDefault: CaseClassDefault$ = 
  new CaseClassDefault$()
final module class CaseClassDefault$() extends AnyRef() { 
  this: CaseClassDefault.type =>
  def apply(value: Int): CaseClassDefault = new CaseClassDefault(value)
  def unapply(x$1: CaseClassDefault): CaseClassDefault = x$1
  override def toString: String = "CaseClassDefault"
  def $lessinit$greater$default$1: Int @uncheckedVariance = 1
}

[bishabosha]

this looks by design in Applications, but it is an incompatibility
https://github.com/lampepfl/dotty/blob/45ce129a2c166a6fbb64dc096fe50435f1f77f96/compiler/src/dotty/tools/dotc/typer/Applications.scala#L223

[odersky]

Yes, synthesized apply methods take the default getters of their constructors. If we did not want to do that, we would either make apply methods useless, or have to duplicate all default getters. I believe it is better this way. Can Tasty reader be adapted to deal with it?

[bishabosha]

Can Tasty reader be adapted to deal with it?

It should be possible, I am looking into it

[bishabosha]

PR open here scala/scala#9730

[odersky]

Great! @bishabosha Can I leave the issue here for to you to close once the scala/scala side is resolved?

[TheElectronWill]

scala/scala#9730 has been closed, so this issue should be closed too?

[bishabosha]

perhaps an extra note in the documentation about the dropping of generation of default parameter forwarders for synthetic apply methods is required