Inconsistent `export` of case classes' synthetic methods

Compiler version

3.0.1

Minimized code

case class User(name: String)

case class RegisteredUser(id: String, data: User) {
  export data.*
}

@main def app() = 
  println(RegisteredUser("Id", User("Name"))) // RegisteredUser(Name)
  println(RegisteredUser("Id", User("Name")).canEqual(User("Name"))) // True
  // The rest works as expected
  println(RegisteredUser("Id", User("Name")) == User("Name")) // False
  println(RegisteredUser("Id", User("Name")).hashCode == User("Name").hashCode) // False

Output

RegisteredUser(Name)
true
false
false

Expectation

RegisteredUser(Id, User(Name))
false
false
false

According to @bishabosha

So what’s happening here is that productArity and productElement are delegated to data field, (those methods are called from toString) but equals, hashCode, toString are not exported. (problematic that canEqual is also exported)

and @kubukoz

Yeah, strange. toString defers to productPrefix I think, that should probably have been exported as well…

[1] https://twitter.com/bishabosha/status/1421803014722052098 [2] https://twitter.com/kubukoz/status/1421810894967906304

[smarter]

I think we do have a problem here because the result is not consistent under separate compilation, if I split the example into a file containing just:

case class User(name: String)

which I then compile, followed by compiling the rest of the example I get:

RegisteredUser(Id,User(Name))
false
false
false

because the PostTyper phase added synthetic definitions for canEqual/productXXX and wildcard exports filters synthetic definitions out: https://github.com/lampepfl/dotty/blob/9e8d5c55153fdbe0d3f78d661cb3b51113403128/compiler/src/dotty/tools/dotc/typer/Namer.scala#L1159

[odersky]

@smarter Fair point 😃