CanBuildFrom/GenTraversableFactory causing serialization issue

[nevillelyh]

I can reproduce with the following code on scala 2.12.

import java.io.{ByteArrayOutputStream, ObjectOutputStream}

import org.scalacheck._

object SerDe {
  def main(args: Array[String]): Unit = {
    val oos = new ObjectOutputStream(new ByteArrayOutputStream)

    val arbInt = implicitly[Arbitrary[Int]]
    oos.writeObject(arbInt)

    val arbList = implicitly[Arbitrary[List[Int]]]
    oos.writeObject(arbList)
  }
}

Looks like it's summoning the following implicit in BuildableVersionSpecific.

implicit def buildableCanBuildFrom[T,F,C](implicit c: CanBuildFrom[F,T,C]): Buildable[T,C]

And I can see one for list in SerializableCanBuildFroms

implicit def listCanBuildFrom[T]: CanBuildFrom[List[T], T, List[T]]

But somehow it's not summoned.

Stack trace:

[error] (run-main-2) java.io.NotSerializableException: scala.collection.generic.GenTraversableFactory$$anon$1
[error] java.io.NotSerializableException: scala.collection.generic.GenTraversableFactory$$anon$1
[error]         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
[error]         at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
[error]         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
[error]         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
[error]         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178) scalacheck / Test / runMain 0s
[error]         at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1378)
[error]         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
[error]         at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
[error]         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
[error]         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
[error]         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
[error]         at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
[error]         at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
[error]         at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
[error]         at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
[error]         at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
[error]         at magnolia.scalacheck.test.SerDe$.main(SerDe.scala:15)
[error]         at magnolia.scalacheck.test.SerDe.main(SerDe.scala)
[error]         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error]         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error]         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error]         at java.lang.reflect.Method.invoke(Method.java:498)

[nevillelyh]

Adding import org.scalacheck.util.SerializableCanBuildFroms._ fixes the issue. Is it by design that they're not in scope?

[ashawley]

There's a serializability test in ScalaCheck that works. Ironically, the import you needed was removed from that test in d8f1322. I know forking the JVM was needed for the test to work in Scala 2.13, but you're asking about 2.12, so I'm not sure why you need the import.

[nevillelyh]

That test you linked doesn't cover Arbitrary[List[T]] though, which summons CanBuildFrom transitively. So it was probably an unused import. Forking for 2.13 might be a different issue since CanBuildFrom was replaced with Factory which is serializable.

So it does look like these implicits need to be manually imported.

[ashawley]

Yes, a test of Arbitrary[List[T]] is missing. Good catch. For that test, it would require that import statement.