[SPARK-17761][SQL] Remove MutableRow

## What changes were proposed in this pull request?
In practice we cannot guarantee that an `InternalRow` is immutable. This makes the `MutableRow` almost redundant. This PR folds `MutableRow` into `InternalRow`.

The code below illustrates the immutability issue with InternalRow:
```scala
import org.apache.spark.sql.catalyst.InternalRow
import org.apache.spark.sql.catalyst.expressions.GenericMutableRow
val struct = new GenericMutableRow(1)
val row = InternalRow(struct, 1)
println(row)
scala> [[null], 1]
struct.setInt(0, 42)
println(row)
scala> [[42], 1]
```

This might be somewhat controversial, so feedback is appreciated.

## How was this patch tested?
Existing tests.

Author: Herman van Hovell <hvanhovell@databricks.com>

Closes #15333 from hvanhovell/SPARK-17761.

4 files changed, 10 insertions, 10 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/linalg/MatrixUDT.scala b/mllib/src/main/scala/org/apache/spark/ml/linalg/MatrixUDT.scala
index a1e53662f0..f4a8556c71 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/linalg/MatrixUDT.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/linalg/MatrixUDT.scala
@@ -18,7 +18,7 @@
 package org.apache.spark.ml.linalg
 
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.expressions.{GenericMutableRow, UnsafeArrayData}
+import org.apache.spark.sql.catalyst.expressions.{GenericInternalRow, UnsafeArrayData}
 import org.apache.spark.sql.types._
 
 /**
@@ -46,7 +46,7 @@ private[spark] class MatrixUDT extends UserDefinedType[Matrix] {
   }
 
   override def serialize(obj: Matrix): InternalRow = {
-    val row = new GenericMutableRow(7)
+    val row = new GenericInternalRow(7)
     obj match {
       case sm: SparseMatrix =>
         row.setByte(0, 0)
diff --git a/mllib/src/main/scala/org/apache/spark/ml/linalg/VectorUDT.scala b/mllib/src/main/scala/org/apache/spark/ml/linalg/VectorUDT.scala
index 0b9b2ff5c5..917861309c 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/linalg/VectorUDT.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/linalg/VectorUDT.scala
@@ -18,7 +18,7 @@
 package org.apache.spark.ml.linalg
 
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.expressions.{GenericMutableRow, UnsafeArrayData}
+import org.apache.spark.sql.catalyst.expressions.{GenericInternalRow, UnsafeArrayData}
 import org.apache.spark.sql.types._
 
 /**
@@ -42,14 +42,14 @@ private[spark] class VectorUDT extends UserDefinedType[Vector] {
   override def serialize(obj: Vector): InternalRow = {
     obj match {
       case SparseVector(size, indices, values) =>
-        val row = new GenericMutableRow(4)
+        val row = new GenericInternalRow(4)
         row.setByte(0, 0)
         row.setInt(1, size)
         row.update(2, UnsafeArrayData.fromPrimitiveArray(indices))
         row.update(3, UnsafeArrayData.fromPrimitiveArray(values))
         row
       case DenseVector(values) =>
-        val row = new GenericMutableRow(4)
+        val row = new GenericInternalRow(4)
         row.setByte(0, 1)
         row.setNullAt(1)
         row.setNullAt(2)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala
index 6642999a21..542a69b3ef 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala
@@ -28,7 +28,7 @@ import com.github.fommil.netlib.BLAS.{getInstance => blas}
 import org.apache.spark.annotation.Since
 import org.apache.spark.ml.{linalg => newlinalg}
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.expressions.{GenericMutableRow, UnsafeArrayData}
+import org.apache.spark.sql.catalyst.expressions.{GenericInternalRow, UnsafeArrayData}
 import org.apache.spark.sql.types._
 
 /**
@@ -189,7 +189,7 @@ private[spark] class MatrixUDT extends UserDefinedType[Matrix] {
   }
 
   override def serialize(obj: Matrix): InternalRow = {
-    val row = new GenericMutableRow(7)
+    val row = new GenericInternalRow(7)
     obj match {
       case sm: SparseMatrix =>
         row.setByte(0, 0)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
index 91f065831c..fbd217af74 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
@@ -34,7 +34,7 @@ import org.apache.spark.annotation.{AlphaComponent, Since}
 import org.apache.spark.ml.{linalg => newlinalg}
 import org.apache.spark.mllib.util.NumericParser
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.expressions.{GenericMutableRow, UnsafeArrayData}
+import org.apache.spark.sql.catalyst.expressions.{GenericInternalRow, UnsafeArrayData}
 import org.apache.spark.sql.types._
 
 /**
@@ -214,14 +214,14 @@ class VectorUDT extends UserDefinedType[Vector] {
   override def serialize(obj: Vector): InternalRow = {
     obj match {
       case SparseVector(size, indices, values) =>
-        val row = new GenericMutableRow(4)
+        val row = new GenericInternalRow(4)
         row.setByte(0, 0)
         row.setInt(1, size)
         row.update(2, UnsafeArrayData.fromPrimitiveArray(indices))
         row.update(3, UnsafeArrayData.fromPrimitiveArray(values))
         row
       case DenseVector(values) =>
-        val row = new GenericMutableRow(4)
+        val row = new GenericInternalRow(4)
         row.setByte(0, 1)
         row.setNullAt(1)
         row.setNullAt(2)