[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.

1 files changed, 35 insertions, 0 deletions

diff --git a/python/pyspark/sql/tests.py b/python/pyspark/sql/tests.py
index a8ca386e1c..87dbb50495 100644
--- a/python/pyspark/sql/tests.py
+++ b/python/pyspark/sql/tests.py
@@ -575,6 +575,41 @@ class SQLTests(ReusedPySparkTestCase):
         _verify_type(PythonOnlyPoint(1.0, 2.0), PythonOnlyUDT())
         self.assertRaises(ValueError, lambda: _verify_type([1.0, 2.0], PythonOnlyUDT()))
 
+    def test_simple_udt_in_df(self):
+        schema = StructType().add("key", LongType()).add("val", PythonOnlyUDT())
+        df = self.spark.createDataFrame(
+            [(i % 3, PythonOnlyPoint(float(i), float(i))) for i in range(10)],
+            schema=schema)
+        df.show()
+
+    def test_nested_udt_in_df(self):
+        schema = StructType().add("key", LongType()).add("val", ArrayType(PythonOnlyUDT()))
+        df = self.spark.createDataFrame(
+            [(i % 3, [PythonOnlyPoint(float(i), float(i))]) for i in range(10)],
+            schema=schema)
+        df.collect()
+
+        schema = StructType().add("key", LongType()).add("val",
+                                                         MapType(LongType(), PythonOnlyUDT()))
+        df = self.spark.createDataFrame(
+            [(i % 3, {i % 3: PythonOnlyPoint(float(i + 1), float(i + 1))}) for i in range(10)],
+            schema=schema)
+        df.collect()
+
+    def test_complex_nested_udt_in_df(self):
+        from pyspark.sql.functions import udf
+
+        schema = StructType().add("key", LongType()).add("val", PythonOnlyUDT())
+        df = self.spark.createDataFrame(
+            [(i % 3, PythonOnlyPoint(float(i), float(i))) for i in range(10)],
+            schema=schema)
+        df.collect()
+
+        gd = df.groupby("key").agg({"val": "collect_list"})
+        gd.collect()
+        udf = udf(lambda k, v: [(k, v[0])], ArrayType(df.schema))
+        gd.select(udf(*gd)).collect()
+
     def test_udt_with_none(self):
         df = self.spark.range(0, 10, 1, 1)