Dotty: Wildcard export ignores synthetic members generated from desugaring

[eloots]

Minimized code

Up-to Scala 3.0.0-M2, a wildcard export worked as expected: ALL members were exported, both singleton members as class case members:

object T:
  enum Command:
    case ResetSudokuDetailState
    case Update(cellUpdates: Int)
    case GetSudokuDetailState(z:Int)
  export Command._

val update = T.Update(cellUpdates = 5)

In Scala 3.0.0-M3, the above code exports ResetSudokuDetailState, but not Update and GetSudokuDetailState.

The workaround is to export all members explicitly:

object T:
  enum Command:
    case ResetSudokuDetailState
    case Update(cellUpdates: Int)
    case GetSudokuDetailState(z:Int)
  export Command.{ResetSudokuDetailState, Update, GetSudokuDetailState}

val update = T.Update(cellUpdates = 5)

Output

scala> object T:
     |   enum Command:
     |     case ResetSudokuDetailState
     |     case Update(cellUpdates: Int)
     |     case GetSudokuDetailState(z:Int)
     |   export Command._
     |
     | val update = T.Update(cellUpdates = 5)
8 |val update = T.Update(cellUpdates = 5)
  |             ^^^^^^^^
  |             value Update is not a member of object T

Expectation

Doing a wildcard export on an enum should export _all_ members

[bishabosha]

I think this may have something to do with creator application changes, if you take a look suing -Xprint:typer cli option, the companion objects of enum cases were never exported, (I checked back to 0.25.0), just type aliases, so T.Update(cellUpdates = 5) was actually a creator application and not calling T.Update.apply.

[bishabosha]

more bad news, it seems you cant wildcard export definitions that are added after desugaring:

object T:
  object Command:
    case class Update(cellUpdates: Int)
  export Command._

in this example the synthetic companion object for Update is also not exported.

Will need to investigate if this is a fundamental issue with export desugaring at Namer or if there are just missing wildcard definitions being ignored

[eloots]

more bad news, it seems you cant wildcard export definitions that are added after desugaring

That's a pity... Using export to export all members of an enum makes it possible to take Scala 2 ADTs encoded with sealed traits; trivially encode them as Scala 3 enum's and leave any code that uses them unmodified.
Not having this work as it [accidentally] did prior to M3 means that code has to be changed at the use site.

[odersky]

It's a conscious decision not to export synthetic members. One positive aspect of this is that you can export all cases from an enum without also exporting the synthetic values etc machinery. I think we will stick to that.

[bishabosha]

@odersky would it be desirable to treat the non-(private/synthetic) symbols as names that can then be reinterpreted as an explicit selector, which would then pick up the companion object of case classes?

[odersky]

@bishabosha Yes, I think that could work. I.e. if one of a pair of type/term definitions with the same name is non-synthatic, the other is imported as well.