[SPARK-48774][SQL] Use SparkSession in SQLImplicits

mllib/src/test/scala/org/apache/spark/mllib/util/MLlibTestSparkContext.scala

@@ -69,7 +69,7 @@ trait MLlibTestSparkContext extends TempDirectory { self: Suite =>
    * but the implicits import is needed in the constructor.
    */
   protected object testImplicits extends SQLImplicits {
-    protected override def _sqlContext: SQLContext = self.spark.sqlContext
+    protected override def session: SparkSession = self.spark
   }
 
   private[spark] def standardize(instances: Array[Instance]): Array[Instance] = {

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

@@ -252,7 +252,7 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @since 1.3.0
    */
   object implicits extends SQLImplicits with Serializable {
-    protected override def _sqlContext: SQLContext = self
+    protected override def session: SparkSession = self.sparkSession
   }
   // scalastyle:on
 

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

@@ -31,7 +31,7 @@ import org.apache.spark.sql.catalyst.encoders.ExpressionEncoder
  */
 abstract class SQLImplicits extends LowPrioritySQLImplicits {
 
-  protected def _sqlContext: SQLContext
+  protected def session: SparkSession
 
   /**
    * Converts $"col name" into a [[Column]].
@@ -242,15 +242,15 @@ abstract class SQLImplicits extends LowPrioritySQLImplicits {
    * @since 1.6.0
    */
   implicit def rddToDatasetHolder[T : Encoder](rdd: RDD[T]): DatasetHolder[T] = {
-    DatasetHolder(_sqlContext.createDataset(rdd))
+    DatasetHolder(session.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))
+    DatasetHolder(session.createDataset(s))
   }
 
   /**

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

@@ -846,7 +846,7 @@ class SparkSession private(
    * @since 2.0.0
    */
   object implicits extends SQLImplicits with Serializable {
-    protected override def _sqlContext: SQLContext = SparkSession.this.sqlContext
+    protected override def session: SparkSession = SparkSession.this
   }
   // scalastyle:on
 

sql/core/src/main/scala/org/apache/spark/sql/expressions/scalalang/typed.scala

@@ -41,7 +41,7 @@ object typed {
 
   // TODO: This is pretty hacky. Maybe we should have an object for implicit encoders.
   private val implicits = new SQLImplicits {
-    override protected def _sqlContext: SQLContext = null
+    override protected def session: SparkSession = null
   }
 
   /**

sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestData.scala

@@ -35,7 +35,7 @@ private[sql] trait SQLTestData { self =>
 
   // Helper object to import SQL implicits without a concrete SQLContext
   private object internalImplicits extends SQLImplicits {
-    protected override def _sqlContext: SQLContext = self.spark.sqlContext
+    protected override def session: SparkSession = self.spark
   }
 
   import internalImplicits._

sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala

@@ -240,7 +240,7 @@ private[sql] trait SQLTestUtilsBase
    * but the implicits import is needed in the constructor.
    */
   protected object testImplicits extends SQLImplicits {
-    protected override def _sqlContext: SQLContext = self.spark.sqlContext
+    protected override def session: SparkSession = self.spark
   }
 
   protected override def withSQLConf[T](pairs: (String, String)*)(f: => T): T = {