[SPARK-20274][SQL] support compatible array element type in encoder

## What changes were proposed in this pull request?

This is a regression caused by SPARK-19716.

Before SPARK-19716, we will cast an array field to the expected array type. However, after SPARK-19716, the cast is removed, but we forgot to push the cast to the element level.

## How was this patch tested?

new regression tests

Author: Wenchen Fan <[email protected]>

Closes apache#17587 from cloud-fan/array.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/ScalaReflection.scala

@@ -132,7 +132,7 @@ object ScalaReflection extends ScalaReflection {
   def deserializerFor[T : TypeTag]: Expression = {
     val tpe = localTypeOf[T]
     val clsName = getClassNameFromType(tpe)
-    val walkedTypePath = s"""- root class: "${clsName}"""" :: Nil
+    val walkedTypePath = s"""- root class: "$clsName"""" :: Nil
     deserializerFor(tpe, None, walkedTypePath)
   }
 
@@ -270,12 +270,14 @@ object ScalaReflection extends ScalaReflection {
 
       case t if t <:< localTypeOf[Array[_]] =>
         val TypeRef(_, _, Seq(elementType)) = t
-        val Schema(_, elementNullable) = schemaFor(elementType)
+        val Schema(dataType, elementNullable) = schemaFor(elementType)
         val className = getClassNameFromType(elementType)
         val newTypePath = s"""- array element class: "$className"""" +: walkedTypePath
 
-        val mapFunction: Expression => Expression = p => {
-          val converter = deserializerFor(elementType, Some(p), newTypePath)
+        val mapFunction: Expression => Expression = element => {
+          // upcast the array element to the data type the encoder expected.
+          val casted = upCastToExpectedType(element, dataType, newTypePath)
+          val converter = deserializerFor(elementType, Some(casted), newTypePath)
           if (elementNullable) {
             converter
           } else {
@@ -305,12 +307,14 @@ object ScalaReflection extends ScalaReflection {
 
       case t if t <:< localTypeOf[Seq[_]] =>
         val TypeRef(_, _, Seq(elementType)) = t
-        val Schema(_, elementNullable) = schemaFor(elementType)
+        val Schema(dataType, elementNullable) = schemaFor(elementType)
         val className = getClassNameFromType(elementType)
         val newTypePath = s"""- array element class: "$className"""" +: walkedTypePath
 
-        val mapFunction: Expression => Expression = p => {
-          val converter = deserializerFor(elementType, Some(p), newTypePath)
+        val mapFunction: Expression => Expression = element => {
+          // upcast the array element to the data type the encoder expected.
+          val casted = upCastToExpectedType(element, dataType, newTypePath)
+          val converter = deserializerFor(elementType, Some(casted), newTypePath)
           if (elementNullable) {
             converter
           } else {

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -26,7 +26,7 @@ import org.apache.spark.sql.catalyst.catalog._
 import org.apache.spark.sql.catalyst.encoders.OuterScopes
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.expressions.aggregate._
-import org.apache.spark.sql.catalyst.expressions.objects.{MapObjects, NewInstance, UnresolvedMapObjects}
+import org.apache.spark.sql.catalyst.expressions.objects.{LambdaVariable, MapObjects, NewInstance, UnresolvedMapObjects}
 import org.apache.spark.sql.catalyst.expressions.SubExprUtils._
 import org.apache.spark.sql.catalyst.optimizer.BooleanSimplification
 import org.apache.spark.sql.catalyst.plans._
@@ -2321,7 +2321,11 @@ class Analyzer(
    */
   object ResolveUpCast extends Rule[LogicalPlan] {
     private def fail(from: Expression, to: DataType, walkedTypePath: Seq[String]) = {
-      throw new AnalysisException(s"Cannot up cast ${from.sql} from " +
+      val fromStr = from match {
+        case l: LambdaVariable => "array element"
+        case e => e.sql
+      }
+      throw new AnalysisException(s"Cannot up cast $fromStr from " +
         s"${from.dataType.simpleString} to ${to.simpleString} as it may truncate\n" +
         "The type path of the target object is:\n" + walkedTypePath.mkString("", "\n", "\n") +
         "You can either add an explicit cast to the input data or choose a higher precision " +

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/encoders/EncoderResolutionSuite.scala

@@ -33,6 +33,8 @@ case class StringIntClass(a: String, b: Int)
 
 case class ComplexClass(a: Long, b: StringLongClass)
 
+case class PrimitiveArrayClass(arr: Array[Long])
+
 case class ArrayClass(arr: Seq[StringIntClass])
 
 case class NestedArrayClass(nestedArr: Array[ArrayClass])
@@ -66,6 +68,27 @@ class EncoderResolutionSuite extends PlanTest {
     encoder.resolveAndBind(attrs).fromRow(InternalRow(InternalRow(str, 1.toByte), 2))
   }
 
+  test("real type doesn't match encoder schema but they are compatible: primitive array") {
+    val encoder = ExpressionEncoder[PrimitiveArrayClass]
+    val attrs = Seq('arr.array(IntegerType))
+    val array = new GenericArrayData(Array(1, 2, 3))
+    encoder.resolveAndBind(attrs).fromRow(InternalRow(array))
+  }
+
+  test("the real type is not compatible with encoder schema: primitive array") {
+    val encoder = ExpressionEncoder[PrimitiveArrayClass]
+    val attrs = Seq('arr.array(StringType))
+    assert(intercept[AnalysisException](encoder.resolveAndBind(attrs)).message ==
+      s"""
+         |Cannot up cast array element from string to bigint as it may truncate
+         |The type path of the target object is:
+         |- array element class: "scala.Long"
+         |- field (class: "scala.Array", name: "arr")
+         |- root class: "org.apache.spark.sql.catalyst.encoders.PrimitiveArrayClass"
+         |You can either add an explicit cast to the input data or choose a higher precision type
+       """.stripMargin.trim + " of the field in the target object")
+  }
+
   test("real type doesn't match encoder schema but they are compatible: array") {
     val encoder = ExpressionEncoder[ArrayClass]
     val attrs = Seq('arr.array(new StructType().add("a", "int").add("b", "int").add("c", "int")))