Separate compilation with value class fails due to missing companion object

[smarter]

A_1.scala:

class A(val self: Double) extends AnyVal

B_2.scala:

object B {
  def foo: A = new A(1)
}

% ./bin/dotc A_1.scala
% ./bin/dotc B_2.scala
exception occurred while compiling B.scala
Exception in thread "main" java.lang.AssertionError: NoDenotation.owner
        at dotty.tools.dotc.core.SymDenotations$NoDenotation.owner(SymDenotations.scala:1799)
        at dotty.tools.dotc.ast.tpd$.ref(tpd.scala:346)
        at dotty.tools.dotc.transform.Erasure$Boxing$.cast(Erasure.scala:230)
        at dotty.tools.dotc.transform.Erasure$Boxing$$anonfun$unbox$2.apply(Erasure.scala:200)
        at dotty.tools.dotc.transform.Erasure$Boxing$$anonfun$unbox$2.apply(Erasure.scala:175)
...

This does not happen if I manually create a companion in A_1.scala:

class A(val self: Double) extends AnyVal
object A

[odersky]

I guess this is due to the recent changes where we create companion objects only when we know they will be needed. @DarkDimius do you agree?

[smarter]

@odersky : I tried to set needsCompanion to true in FirstTransform so that we always generate companions and the issue still manifest itself. @DarkDimius suggested that the issue is that FirstTransform only operates on trees, not types, and when we unpickle A we only transform its type, so we never add its missing companion.

[DarkDimius]

@odersky that's indeed independent from the recent change.
I have suggested @VladimirNik to try to move creation of symbols for companion objects to info-transformer of FirstTransform.

[odersky]

Question to clarify:

The problem arises specifically when we read a value class from another
dotty module via TASTY? It does not arise when unpickling Scala 2 value
classes?

On Thu, Mar 3, 2016 at 8:28 PM, Dmitry Petrashko notifications@github.com
wrote:

@odersky https://github.com/odersky that's indeed independent for the
recent change.
I have suggested @VladimirNik https://github.com/VladimirNik to try to
move creation of symbols for companion objects to info-transformer of
FirstTransform.

—
Reply to this email directly or view it on GitHub
#1137 (comment).

Martin Odersky
EPFL

[smarter]

@odersky : Just tried it, looks like compiling A_1.scala with scalac then B_2.scala with dotc works correctly.

[DarkDimius]

@odersky note that Scala2Unpicker has its own mechanism for registering class companions.
We could indeed create a similar one in TastyUnpickler, but It will duplicate the functionality already present in FirstTransform. Making a small change to FirstTransform not to change types using side-effect-full enteredAfter and instead be a proper InfoTransformer seems like a better design to me. It would additionally allow to put more phases that need companions in the same mini-phase block in future, unlike now when only phases in next blocks could rely on the guarantees of FirstTransform.