Bug: Encoder cannot be found when a tuple component is a type alias for an Array
Status: Resolved | Priority: Major | Resolution: Fixed
Created: 27/Jan/22 08:23
Affects Version/s: 3.1.2

ScalaReflection.dataTypeFor fails when Array[T] has been aliased for some T, and then the alias is being used as a component of e.g. a product.

Minimal example, tested in version 3.1.2:
{code:java}
type Data = Array[Long]
val xs:List[(Data,Int)] = List((Array(1),1), (Array(2),2))
sc.parallelize(xs).toDF("a", "b"){code}
This gives the following exception:
{code:java}
scala.MatchError: Data (of class scala.reflect.internal.Types$AliasNoArgsTypeRef) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.$anonfun$dataTypeFor$1(ScalaReflection.scala:104) 
 at scala.reflect.internal.tpe.TypeConstraints$UndoLog.undo(TypeConstraints.scala:69) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects(ScalaReflection.scala:904) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects$(ScalaReflection.scala:903) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.cleanUpReflectionObjects(ScalaReflection.scala:49) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.dataTypeFor(ScalaReflection.scala:88) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.$anonfun$serializerFor$6(ScalaReflection.scala:573) 
 at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:238) 
 at scala.collection.immutable.List.foreach(List.scala:392) 
 at scala.collection.TraversableLike.map(TraversableLike.scala:238) 
 at scala.collection.TraversableLike.map$(TraversableLike.scala:231) 
 at scala.collection.immutable.List.map(List.scala:298) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.$anonfun$serializerFor$1(ScalaReflection.scala:562) 
 at scala.reflect.internal.tpe.TypeConstraints$UndoLog.undo(TypeConstraints.scala:69) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects(ScalaReflection.scala:904) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects$(ScalaReflection.scala:903) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.cleanUpReflectionObjects(ScalaReflection.scala:49) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.serializerFor(ScalaReflection.scala:432) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.$anonfun$serializerForType$1(ScalaReflection.scala:421) 
 at scala.reflect.internal.tpe.TypeConstraints$UndoLog.undo(TypeConstraints.scala:69) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects(ScalaReflection.scala:904) 
 at org.apache.spark.sql.catalyst.ScalaReflection.cleanUpReflectionObjects$(ScalaReflection.scala:903) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.cleanUpReflectionObjects(ScalaReflection.scala:49) 
 at org.apache.spark.sql.catalyst.ScalaReflection$.serializerForType(ScalaReflection.scala:413) 
 at org.apache.spark.sql.catalyst.encoders.ExpressionEncoder$.apply(ExpressionEncoder.scala:55) 
 at org.apache.spark.sql.Encoders$.product(Encoders.scala:285) 
 at org.apache.spark.sql.LowPrioritySQLImplicits.newProductEncoder(SQLImplicits.scala:251) 
 at org.apache.spark.sql.LowPrioritySQLImplicits.newProductEncoder$(SQLImplicits.scala:251) 
 at org.apache.spark.sql.SQLImplicits.newProductEncoder(SQLImplicits.scala:32) 
 ... 48 elided{code}
At first glance, I think this could be fixed by changing e.g.
{code:java}
getClassNameFromType(tpe) to 
getClassNameFromType(tpe.dealias)
{code}
in ScalaReflection.dataTypeFor. I will try to test that and submit a pull request shortly.