attempting to use runtimereplaceable

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala

@@ -1046,6 +1046,28 @@ case class ToDate(child: Expression) extends UnaryExpression with ImplicitCastIn
   override def prettyName: String = "to_date"
 }
 
+/**
+ * Parses a column with a format to a timestamp.
+ */
+@ExpressionDescription(
+  usage = "_FUNC_(timestamp, fmt) - Parses the `timestamp` expression with the `fmt` expression.",
+  extended = """
+    Examples:
+      > SELECT _FUNC_('2016-12-31', 'yyyy-MM-dd');
+       1483142400
+  """)
+case class ToTimestamp(left: Expression, right: Expression, child: Expression)
+  extends RuntimeReplaceable {
+
+  def this(left: Expression, right: Expression) = {
+  this(left, right, UnixTimestamp(left, right))
+}
+
+  override def dataType: DataType = TimestampType
+  override def flatArguments: Iterator[Any] = Iterator(left, right)
+  override def sql: String = s"$prettyName(${left.sql}, ${right.sql})"
+}
+
 /**
  * Returns date truncated to the unit specified by the format.
  */

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

@@ -2667,9 +2667,7 @@ object functions {
    * @group datetime_funcs
    * @since 2.2.0
    */
-  def to_timestamp(s: Column, p: String): Column = {
-    withExpr {UnixTimestamp(s.expr, Literal(p)) }.cast("timestamp")
-  }
+  def to_timestamp(s: Column, p: String): Column = withExpr {ToTimestamp(s.expr, Literal(p)) }
 
   /**
    * Converts the column into DateType.