Cannot deserialize scala.collection.generic.DefaultSerializationProxy in Scala 2.13.0-M5

[xerial]

When trying to deserialize a case class that contains a Scala collection (e.g., Seq, Vector) of case objects, java.io.ObjectInputStream throws an error Cannot assign instance of scala.collection.generic.DefaultSerializationProxy to field to ....

How to reproduce

build.sbt

scalaVersion := "2.13.0-M5"
// fork in run := true    // uncomment this to resolve this error

SerdeTest.scala
https://gist.github.com/xerial/58e14b21a4492d6f87765fe9bff4b61a

sealed trait Color
case object RED extends Color
case class A(colors:Seq[Color]) // Deserialization of A fails

$ sbt run
[info] Running serde.SerdeTest
[error] (run-main-14) java.lang.ClassCastException: cannot assign instance of scala.collection.generic.DefaultSerializationProxy to field serde.A.colors of type scala.collection.immutable.Seq in instance of serde.A
[error] java.lang.ClassCastException: cannot assign instance of scala.collection.generic.DefaultSerializationProxy to field serde.A.colors of type scala.collection.immutable.Seq in instance of serde.A
[error] 	at java.io.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2287)
[error] 	at java.io.ObjectStreamClass.setObjFieldValues(ObjectStreamClass.java:1417)
[error] 	at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2293)
[error] 	at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
[error] 	at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
[error] 	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
[error] 	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
[error] 	at serde.SerdeTest$.deserialize(SerdeTest.scala:22)
[error] 	at serde.SerdeTest$.main(SerdeTest.scala:29)
[error] 	at serde.SerdeTest.main(SerdeTest.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)
[error] Nonzero exit code: 1
[error] (Compile / run) Nonzero exit code: 1

Related issues:

• investigate possible serialization regression(s) in 2.13 milestones scala-dev#562
• Can't deserialize scala.List[M] if scala-library is not in the same classloader as M #9237
• ClassNotFoundException during readObject() sbt/sbt#89

[retronym]

This appears to be a different symptom of the same root cause.

ObjectInputStream encounters an java.lang.ClassNotFoundException: serde.RED$, which it records internally for later reporting.

This seems to prevent the use of the readResolve method:

    /**
     * If resolveObject has been enabled and given object does not have an
     * exception associated with it, calls resolveObject to determine
     * replacement for object, and updates handle table accordingly.  Returns
     * replacement object, or echoes provided object if no replacement
     * occurred.  Expects that passHandle is set to given object's handle prior
     * to calling this method.
     */
    private Object checkResolve(Object obj) throws IOException {
        if (!enableResolve || handles.lookupException(passHandle) != null) {
            return obj;
        }
        Object rep = resolveObject(obj);

Which leads to the ClassCastException obscuring the root cause.

[szeiger]

Closing as duplicate of #9237