[SPARK-11485][SQL] Make DataFrameHolder and DatasetHolder public.

These two classes should be public, since they are used in public code.

Author: Reynold Xin <rxin@databricks.com>

Closes #9445 from rxin/SPARK-11485.

project/MimaExcludes.scala

@@ -161,6 +161,9 @@ object MimaExcludes {
           "org.apache.spark.sql.UDFRegistration.org$apache$spark$sql$UDFRegistration$$builder$23"),
         ProblemFilters.exclude[MissingMethodProblem](
           "org.apache.spark.sql.UDFRegistration.org$apache$spark$sql$UDFRegistration$$builder$24")
+      ) ++ Seq(
+        // SPARK-11485
+        ProblemFilters.exclude[MissingMethodProblem]("org.apache.spark.sql.DataFrameHolder.df")
       )
     case v if v.startsWith("1.5") =>
       Seq(

sql/core/src/main/scala/org/apache/spark/sql/DataFrameHolder.scala

@@ -20,9 +20,14 @@ package org.apache.spark.sql
 /**
  * A container for a [[DataFrame]], used for implicit conversions.
  *
+ * To use this, import implicit conversions in SQL:
+ * {{{
+ *   import sqlContext.implicits._
+ * }}}
+ *
  * @since 1.3.0
  */
-private[sql] case class DataFrameHolder(df: DataFrame) {
+case class DataFrameHolder private[sql](private val df: DataFrame) {
 
   // This is declared with parentheses to prevent the Scala compiler from treating
   // `rdd.toDF("1")` as invoking this toDF and then apply on the returned DataFrame.

sql/core/src/main/scala/org/apache/spark/sql/DatasetHolder.scala

@@ -18,11 +18,16 @@
 package org.apache.spark.sql
 
 /**
- * A container for a [[DataFrame]], used for implicit conversions.
+ * A container for a [[Dataset]], used for implicit conversions.
  *
- * @since 1.3.0
+ * To use this, import implicit conversions in SQL:
+ * {{{
+ *   import sqlContext.implicits._
+ * }}}
+ *
+ * @since 1.6.0
  */
-private[sql] case class DatasetHolder[T](df: Dataset[T]) {
+case class DatasetHolder[T] private[sql](private val df: Dataset[T]) {
 
   // This is declared with parentheses to prevent the Scala compiler from treating
   // `rdd.toDF("1")` as invoking this toDF and then apply on the returned DataFrame.

sql/core/src/main/scala/org/apache/spark/sql/SQLImplicits.scala

@@ -52,6 +52,10 @@ abstract class SQLImplicits {
     DatasetHolder(_sqlContext.createDataset(rdd))
   }
 
+  /**
+   * Creates a [[Dataset]] from a local Seq.
+   * @since 1.6.0
+   */
   implicit def localSeqToDatasetHolder[T : Encoder](s: Seq[T]): DatasetHolder[T] = {
     DatasetHolder(_sqlContext.createDataset(s))
   }