[SPARK-16062] [SPARK-15989] [SQL] Fix two bugs of Python-only UDTs

## What changes were proposed in this pull request?

There are two related bugs of Python-only UDTs. Because the test case of second one needs the first fix too. I put them into one PR. If it is not appropriate, please let me know.

### First bug: When MapObjects works on Python-only UDTs

`RowEncoder` will use `PythonUserDefinedType.sqlType` for its deserializer expression. If the sql type is `ArrayType`, we will have `MapObjects` working on it. But `MapObjects` doesn't consider `PythonUserDefinedType` as its input data type. It causes error like:

    import pyspark.sql.group
    from pyspark.sql.tests import PythonOnlyPoint, PythonOnlyUDT
    from pyspark.sql.types import *

    schema = StructType().add("key", LongType()).add("val", PythonOnlyUDT())
    df = spark.createDataFrame([(i % 3, PythonOnlyPoint(float(i), float(i))) for i in range(10)], schema=schema)
    df.show()

    File "/home/spark/python/lib/py4j-0.10.1-src.zip/py4j/protocol.py", line 312, in get_return_value py4j.protocol.Py4JJavaError: An error occurred while calling o36.showString.
    : java.lang.RuntimeException: Error while decoding: scala.MatchError: org.apache.spark.sql.types.PythonUserDefinedTypef4ceede8 (of class org.apache.spark.sql.types.PythonUserDefinedType)
    ...

### Second bug: When Python-only UDTs is the element type of ArrayType

    import pyspark.sql.group
    from pyspark.sql.tests import PythonOnlyPoint, PythonOnlyUDT
    from pyspark.sql.types import *

    schema = StructType().add("key", LongType()).add("val", ArrayType(PythonOnlyUDT()))
    df = spark.createDataFrame([(i % 3, [PythonOnlyPoint(float(i), float(i))]) for i in range(10)], schema=schema)
    df.show()

## How was this patch tested?
PySpark's sql tests.

Author: Liang-Chi Hsieh <simonh@tw.ibm.com>

Closes #13778 from viirya/fix-pyudt.

2 files changed, 23 insertions, 3 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/RowEncoder.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/RowEncoder.scala
index 67fca153b5..2a6fcd03a2 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/RowEncoder.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/RowEncoder.scala
@@ -206,6 +206,7 @@ object RowEncoder {
     case _: ArrayType => ObjectType(classOf[scala.collection.Seq[_]])
     case _: MapType => ObjectType(classOf[scala.collection.Map[_, _]])
     case _: StructType => ObjectType(classOf[Row])
+    case p: PythonUserDefinedType => externalDataTypeFor(p.sqlType)
     case udt: UserDefinedType[_] => ObjectType(udt.userClass)
   }
 
@@ -220,9 +221,15 @@ object RowEncoder {
     CreateExternalRow(fields, schema)
   }
 
-  private def deserializerFor(input: Expression): Expression = input.dataType match {
+  private def deserializerFor(input: Expression): Expression = {
+    deserializerFor(input, input.dataType)
+  }
+
+  private def deserializerFor(input: Expression, dataType: DataType): Expression = dataType match {
     case dt if ScalaReflection.isNativeType(dt) => input
 
+    case p: PythonUserDefinedType => deserializerFor(input, p.sqlType)
+
     case udt: UserDefinedType[_] =>
       val annotation = udt.userClass.getAnnotation(classOf[SQLUserDefinedType])
       val udtClass: Class[_] = if (annotation != null) {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
index 06589411cf..952a5f3b04 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
@@ -359,6 +359,13 @@ case class LambdaVariable(value: String, isNull: String, dataType: DataType) ext
 object MapObjects {
   private val curId = new java.util.concurrent.atomic.AtomicInteger()
 
+  /**
+   * Construct an instance of MapObjects case class.
+   *
+   * @param function The function applied on the collection elements.
+   * @param inputData An expression that when evaluated returns a collection object.
+   * @param elementType The data type of elements in the collection.
+   */
   def apply(
       function: Expression => Expression,
       inputData: Expression,
@@ -446,8 +453,14 @@ case class MapObjects private(
       case _ => ""
     }
 
+    // The data with PythonUserDefinedType are actually stored with the data type of its sqlType.
+    // When we want to apply MapObjects on it, we have to use it.
+    val inputDataType = inputData.dataType match {
+      case p: PythonUserDefinedType => p.sqlType
+      case _ => inputData.dataType
+    }
 
-    val (getLength, getLoopVar) = inputData.dataType match {
+    val (getLength, getLoopVar) = inputDataType match {
       case ObjectType(cls) if classOf[Seq[_]].isAssignableFrom(cls) =>
         s"${genInputData.value}.size()" -> s"${genInputData.value}.apply($loopIndex)"
       case ObjectType(cls) if cls.isArray =>
@@ -461,7 +474,7 @@ case class MapObjects private(
           s"$seq == null ? $array[$loopIndex] : $seq.apply($loopIndex)"
     }
 
-    val loopNullCheck = inputData.dataType match {
+    val loopNullCheck = inputDataType match {
       case _: ArrayType => s"$loopIsNull = ${genInputData.value}.isNullAt($loopIndex);"
       // The element of primitive array will never be null.
       case ObjectType(cls) if cls.isArray && cls.getComponentType.isPrimitive =>