ClassCastException using distinctOn

[JustinPihony]

DESCRIPTION:

Upon upgrading to Slick 3.3.3 in order to get the #2097 fix for a bug with distinctOn described in #1340 - another case was observed when distinctOn is used for multiple columns (with MySQL) that's now failing with a ClassCastException.:

STEPS TO REPRODUCE:

A sample of the query is below, however the error is transient and

/* Composed from various joins and filters. */
def query: Query[(ClientTable, UserTable, OrganizationUserTable, PhoneTable), (ClientRow, UserRow[Value], OrganizationUserRow, PhoneRow[Value]), Seq] = ???
query
  .map { case (client, user, _, phone) => (client, user, phone) }
  .distinctOn { case (client, user, phone) => (client.id, user.userId, phone.id) }

(In scope are imports from an extension of slick.jdbc.MySQLProfile that provides mappers for various ID wrapper types)

EXPECTED RESULT:

Execute distinctOn without exception

ACTUAL RESULT:

java.lang.ClassCastException: class classpath.to.backend.persistence.UserId cannot be cast to class classpath.to.backend.persistence.ClientId (classpath.to.backend.persistence.UserId and classpath.to.backend.persistence.ClientId are in unnamed module of loader sbt.internal.LayeredClassLoader @9bb579c
[info]  at scala.Function4.$anonfun$tupled$1(Function4.scala:40)
[info]  at slick.relational.TypeMappingResultConverter.read(ResultConverter.scala:134)
[info]  at slick.relational.ProductResultConverter.read(ResultConverter.scala:54)
[info]  at slick.relational.ProductResultConverter.read(ResultConverter.scala:44)
[info]  at slick.jdbc.JdbcInvokerComponent$QueryInvokerImpl.extractValue(JdbcInvokerComponent.scala:36)
[info]  at slick.jdbc.StatementInvoker$$anon$2.extractValue(StatementInvoker.scala:67)
[info]  at slick.jdbc.PositionedResultIterator.fetchNext(PositionedResult.scala:176)
[info]  at slick.util.ReadAheadIterator.update(ReadAheadIterator.scala:28)
[info]  at slick.util.ReadAheadIterator.hasNext(ReadAheadIterator.scala:34)
[info]  at slick.util.ReadAheadIterator.hasNext$(ReadAheadIterator.scala:33)
[info]  at slick.jdbc.PositionedResultIterator.hasNext(PositionedResult.scala:167)
[info]  at slick.jdbc.StreamingInvokerAction.emitStream(StreamingInvokerAction.scala:31)