Change in addition of synthetic Serializable parent to objects with "companion" type alias

[SethTisue]

https://scala-ci.typesafe.com/job/scala-2.12.x-integrate-bootstrap/694/consoleFull

Found 2 binary incompatibilities (11 were filtered out)
=======================================================
 * the type hierarchy of object
   scala.concurrent.forkjoin.package#ThreadLocalRandom is different in current
   version. Missing types {scala.Serializable,java.io.Serializable}
 * the type hierarchy of object
   scala.concurrent.forkjoin.package#ForkJoinTask is different in current
   version. Missing types {scala.Serializable,java.io.Serializable}

[SethTisue]

note that we merged a MiMa version bump for 2.11 at scala/scala#5590 , but I don't think the bump has been merged onto 2.12 yet

[adriaanm]

Looks like a mima bug, maybe in reading pickled info? Both version of the class implement Serializable according to cfr. public static class package.ForkJoinTask. implements Serializable {

[adriaanm]

I'll open a ticket

[retronym]

    def typedModuleDef(mdef: ModuleDef): Tree = {
      // initialize all constructors of the linked class: the type completer (Namer.methodSig)
      // might add default getters to this object. example: "object T; class T(x: Int = 1)"
      val linkedClass = companionSymbolOf(mdef.symbol, context)
      if (linkedClass != NoSymbol)
        linkedClass.info.decl(nme.CONSTRUCTOR).alternatives foreach (_.initialize)

      val clazz     = mdef.symbol.moduleClass
      val typedMods = typedModifiers(mdef.mods)
      assert(clazz != NoSymbol, mdef)
      val noSerializable = (
           (linkedClass eq NoSymbol)
        || linkedClass.isErroneous
        || !linkedClass.isSerializable
        || clazz.isSerializable
      )
      val impl1 = newTyper(context.make(mdef.impl, clazz, newScope)).typedTemplate(mdef.impl, {
        typedParentTypes(mdef.impl) ++ (
          if (noSerializable) Nil
          else {
            clazz.makeSerializable()
            List(TypeTree(SerializableTpe) setPos clazz.pos.focus)
          }
        )
      })

      val impl2  = finishMethodSynthesis(impl1, clazz, context)

      if (settings.isScala211  && mdef.symbol == PredefModule)
        ensurePredefParentsAreInSameSourceFile(impl2)

      treeCopy.ModuleDef(mdef, typedMods, mdef.name, impl2) setType NoType
    }

My recent change to companionSymbolOf is the likely culprit.

[retronym]

Compilation of:

object p1 {
  type A
  object A 
}

Changed in scala/scala#5550, because we no longer treat object A as having a companion class, which for reasons unbeknownst is an input in the logic about whether or not the typer adds scala.Serializable as a synthetic parent.

If we want to retain the bugfix in the compiler, we can workaround by explicitly adding the marker interface, or by whitelisting the change as benign. More conservatively revert the change and defer until 2.13.x.

[som-snytt]

There doesn't seem to be an :aha: emoji.

It's surely traumatic to separate companions like twins and orphaned kittens, so if one is serialized, the other is too; I might need a default ctor arg, another reason it would be nice to have those stashed as statics.

Thx Seth for the heads up; I paid back by answering a newbie on SO.