[SPARK-9085][SQL] Remove LeafNode, UnaryNode, BinaryNode from TreeNode.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala

@@ -50,8 +50,7 @@ case class UnresolvedRelation(
 /**
  * Holds the name of an attribute that has yet to be resolved.
  */
-case class UnresolvedAttribute(nameParts: Seq[String])
-  extends Attribute with trees.LeafNode[Expression] {
+case class UnresolvedAttribute(nameParts: Seq[String]) extends Attribute {
 
   def name: String =
     nameParts.map(n => if (n.contains(".")) s"`$n`" else n).mkString(".")
@@ -96,7 +95,7 @@ case class UnresolvedFunction(name: String, children: Seq[Expression]) extends E
  * Represents all of the input attributes to a given relational operator, for example in
  * "SELECT * FROM ...". A [[Star]] gets automatically expanded during analysis.
  */
-trait Star extends NamedExpression with trees.LeafNode[Expression] {
+abstract class Star extends LeafExpression with NamedExpression {
   self: Product =>
 
   override def name: String = throw new UnresolvedException(this, "name")
@@ -151,7 +150,7 @@ case class UnresolvedStar(table: Option[String]) extends Star {
  * @param names the names to be associated with each output of computing [[child]].
  */
 case class MultiAlias(child: Expression, names: Seq[String])
-  extends NamedExpression with trees.UnaryNode[Expression] {
+  extends UnaryExpression with NamedExpression {
 
   override def name: String = throw new UnresolvedException(this, "name")
 
@@ -210,8 +209,7 @@ case class UnresolvedExtractValue(child: Expression, extraction: Expression)
 /**
  * Holds the expression that has yet to be aliased.
  */
-case class UnresolvedAlias(child: Expression) extends NamedExpression
-  with trees.UnaryNode[Expression] {
+case class UnresolvedAlias(child: Expression) extends UnaryExpression with NamedExpression {
 
   override def toAttribute: Attribute = throw new UnresolvedException(this, "toAttribute")
   override def qualifiers: Seq[String] = throw new UnresolvedException(this, "qualifiers")

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

@@ -30,7 +30,7 @@ import org.apache.spark.sql.types._
  * the layout of intermediate tuples, BindReferences should be run after all such transformations.
  */
 case class BoundReference(ordinal: Int, dataType: DataType, nullable: Boolean)
-  extends NamedExpression with trees.LeafNode[Expression] {
+  extends LeafExpression with NamedExpression {
 
   override def toString: String = s"input[$ordinal]"
 

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

@@ -20,7 +20,6 @@ package org.apache.spark.sql.catalyst.expressions
 import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.catalyst.analysis.{TypeCheckResult, UnresolvedAttribute}
 import org.apache.spark.sql.catalyst.expressions.codegen.{CodeGenContext, GeneratedExpressionCode}
-import org.apache.spark.sql.catalyst.trees
 import org.apache.spark.sql.catalyst.trees.TreeNode
 import org.apache.spark.sql.types._
 

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

@@ -30,8 +30,10 @@ case object Descending extends SortDirection
  * An expression that can be used to sort a tuple.  This class extends expression primarily so that
  * transformations over expression will descend into its child.
  */
-case class SortOrder(child: Expression, direction: SortDirection) extends Expression
-    with trees.UnaryNode[Expression] {
+case class SortOrder(child: Expression, direction: SortDirection) extends UnaryExpression {
+
+  /** Sort order is not foldable because we don't have an eval for it. */
+  override def foldable: Boolean = false
 
   override def dataType: DataType = child.dataType
   override def nullable: Boolean = child.nullable

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

@@ -20,16 +20,20 @@ package org.apache.spark.sql.catalyst.expressions
 import com.clearspring.analytics.stream.cardinality.HyperLogLog
 
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.trees
 import org.apache.spark.sql.catalyst.errors.TreeNodeException
 import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
 import org.apache.spark.sql.catalyst.util.TypeUtils
 import org.apache.spark.sql.types._
 import org.apache.spark.util.collection.OpenHashSet
 
-abstract class AggregateExpression extends Expression {
+trait AggregateExpression extends Expression {
   self: Product =>
 
+  /**
+   * Aggregate expressions should not be foldable.
+   */
+  override def foldable: Boolean = false
+
   /**
    * Creates a new instance that can be used to compute this aggregate expression for a group
    * of input rows/
@@ -60,7 +64,7 @@ case class SplitEvaluation(
  * An [[AggregateExpression]] that can be partially computed without seeing all relevant tuples.
  * These partial evaluations can then be combined to compute the actual answer.
  */
-abstract class PartialAggregate extends AggregateExpression {
+trait PartialAggregate extends AggregateExpression {
   self: Product =>
 
   /**
@@ -74,7 +78,7 @@ abstract class PartialAggregate extends AggregateExpression {
  * [[AggregateExpression]] with an algorithm that will be used to compute one specific result.
  */
 abstract class AggregateFunction
-  extends AggregateExpression with Serializable with trees.LeafNode[Expression] {
+  extends LeafExpression with AggregateExpression with Serializable {
   self: Product =>
 
   /** Base should return the generic aggregate expression that this function is computing */
@@ -91,7 +95,7 @@ abstract class AggregateFunction
   }
 }
 
-case class Min(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Min(child: Expression) extends UnaryExpression with PartialAggregate {
 
   override def nullable: Boolean = true
   override def dataType: DataType = child.dataType
@@ -124,7 +128,7 @@ case class MinFunction(expr: Expression, base: AggregateExpression) extends Aggr
   override def eval(input: InternalRow): Any = currentMin.value
 }
 
-case class Max(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Max(child: Expression) extends UnaryExpression with PartialAggregate {
 
   override def nullable: Boolean = true
   override def dataType: DataType = child.dataType
@@ -157,7 +161,7 @@ case class MaxFunction(expr: Expression, base: AggregateExpression) extends Aggr
   override def eval(input: InternalRow): Any = currentMax.value
 }
 
-case class Count(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Count(child: Expression) extends UnaryExpression with PartialAggregate {
 
   override def nullable: Boolean = false
   override def dataType: LongType.type = LongType
@@ -310,7 +314,7 @@ private[sql] case object HyperLogLogUDT extends UserDefinedType[HyperLogLog] {
 }
 
 case class ApproxCountDistinctPartition(child: Expression, relativeSD: Double)
-  extends AggregateExpression with trees.UnaryNode[Expression] {
+  extends UnaryExpression with AggregateExpression {
 
   override def nullable: Boolean = false
   override def dataType: DataType = HyperLogLogUDT
@@ -340,7 +344,7 @@ case class ApproxCountDistinctPartitionFunction(
 }
 
 case class ApproxCountDistinctMerge(child: Expression, relativeSD: Double)
-  extends AggregateExpression with trees.UnaryNode[Expression] {
+  extends UnaryExpression with AggregateExpression {
 
   override def nullable: Boolean = false
   override def dataType: LongType.type = LongType
@@ -368,7 +372,7 @@ case class ApproxCountDistinctMergeFunction(
 }
 
 case class ApproxCountDistinct(child: Expression, relativeSD: Double = 0.05)
-  extends PartialAggregate with trees.UnaryNode[Expression] {
+  extends UnaryExpression with PartialAggregate {
 
   override def nullable: Boolean = false
   override def dataType: LongType.type = LongType
@@ -386,7 +390,7 @@ case class ApproxCountDistinct(child: Expression, relativeSD: Double = 0.05)
   override def newInstance(): CountDistinctFunction = new CountDistinctFunction(child :: Nil, this)
 }
 
-case class Average(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Average(child: Expression) extends UnaryExpression with PartialAggregate {
 
   override def prettyName: String = "avg"
 
@@ -479,7 +483,7 @@ case class AverageFunction(expr: Expression, base: AggregateExpression)
   }
 }
 
-case class Sum(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Sum(child: Expression) extends UnaryExpression with PartialAggregate {
 
   override def nullable: Boolean = true
 
@@ -606,8 +610,7 @@ case class CombineSumFunction(expr: Expression, base: AggregateExpression)
   }
 }
 
-case class SumDistinct(child: Expression)
-  extends PartialAggregate with trees.UnaryNode[Expression] {
+case class SumDistinct(child: Expression) extends UnaryExpression with PartialAggregate {
 
   def this() = this(null)
   override def nullable: Boolean = true
@@ -701,7 +704,7 @@ case class CombineSetsAndSumFunction(
   }
 }
 
-case class First(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class First(child: Expression) extends UnaryExpression with PartialAggregate {
   override def nullable: Boolean = true
   override def dataType: DataType = child.dataType
   override def toString: String = s"FIRST($child)"
@@ -729,7 +732,7 @@ case class FirstFunction(expr: Expression, base: AggregateExpression) extends Ag
   override def eval(input: InternalRow): Any = result
 }
 
-case class Last(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
+case class Last(child: Expression) extends UnaryExpression with PartialAggregate {
   override def references: AttributeSet = child.references
   override def nullable: Boolean = true
   override def dataType: DataType = child.dataType

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

@@ -40,13 +40,14 @@ import org.apache.spark.sql.types._
  * requested.  The attributes produced by this function will be automatically copied anytime rules
  * result in changes to the Generator or its children.
  */
-abstract class Generator extends Expression {
-  self: Product =>
+trait Generator extends Expression { self: Product =>
 
   // TODO ideally we should return the type of ArrayType(StructType),
   // however, we don't keep the output field names in the Generator.
   override def dataType: DataType = throw new UnsupportedOperationException
 
+  override def foldable: Boolean = false
+
   override def nullable: Boolean = false
 
   /**
@@ -99,8 +100,9 @@ case class UserDefinedGenerator(
 /**
  * Given an input array produces a sequence of rows for each value in the array.
  */
-case class Explode(child: Expression)
-  extends Generator with trees.UnaryNode[Expression] {
+case class Explode(child: Expression) extends UnaryExpression with Generator {
+
+  override def children: Seq[Expression] = child :: Nil
 
   override def checkInputDataTypes(): TypeCheckResult = {
     if (child.dataType.isInstanceOf[ArrayType] || child.dataType.isInstanceOf[MapType]) {
@@ -127,6 +129,4 @@ case class Explode(child: Expression)
         else inputMap.map { case (k, v) => InternalRow(k, v) }
     }
   }
-
-  override def toString: String = s"explode($child)"
 }

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

@@ -37,8 +37,13 @@ object NamedExpression {
  */
 case class ExprId(id: Long)
 
-abstract class NamedExpression extends Expression {
-  self: Product =>
+/**
+ * An [[Expression]] that is named.
+ */
+trait NamedExpression extends Expression { self: Product =>
+
+  /** We should never fold named expressions in order to not remove the alias. */
+  override def foldable: Boolean = false
 
   def name: String
   def exprId: ExprId
@@ -78,8 +83,7 @@ abstract class NamedExpression extends Expression {
     }
 }
 
-abstract class Attribute extends NamedExpression {
-  self: Product =>
+abstract class Attribute extends LeafExpression with NamedExpression { self: Product =>
 
   override def references: AttributeSet = AttributeSet(this)
 
@@ -110,7 +114,7 @@ case class Alias(child: Expression, name: String)(
     val exprId: ExprId = NamedExpression.newExprId,
     val qualifiers: Seq[String] = Nil,
     val explicitMetadata: Option[Metadata] = None)
-  extends NamedExpression with trees.UnaryNode[Expression] {
+  extends UnaryExpression with NamedExpression {
 
   // Alias(Generator, xx) need to be transformed into Generate(generator, ...)
   override lazy val resolved =
@@ -172,7 +176,8 @@ case class AttributeReference(
     nullable: Boolean = true,
     override val metadata: Metadata = Metadata.empty)(
     val exprId: ExprId = NamedExpression.newExprId,
-    val qualifiers: Seq[String] = Nil) extends Attribute with trees.LeafNode[Expression] {
+    val qualifiers: Seq[String] = Nil)
+  extends Attribute {
 
   /**
    * Returns true iff the expression id is the same for both attributes.
@@ -242,7 +247,7 @@ case class AttributeReference(
  * A place holder used when printing expressions without debugging information such as the
  * expression id or the unresolved indicator.
  */
-case class PrettyAttribute(name: String) extends Attribute with trees.LeafNode[Expression] {
+case class PrettyAttribute(name: String) extends Attribute {
 
   override def toString: String = name
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -342,7 +342,7 @@ object ConstantFolding extends Rule[LogicalPlan] {
       case l: Literal => l
 
       // Fold expressions that are foldable.
-      case e if e.foldable => Literal.create(e.eval(null), e.dataType)
+      case e if e.foldable => Literal.create(e.eval(EmptyRow), e.dataType)
 
       // Fold "literal in (item1, item2, ..., literal, ...)" into true directly.
       case In(Literal(v, _), list) if list.exists {
@@ -361,7 +361,7 @@ object OptimizeIn extends Rule[LogicalPlan] {
   def apply(plan: LogicalPlan): LogicalPlan = plan transform {
     case q: LogicalPlan => q transformExpressionsDown {
       case In(v, list) if !list.exists(!_.isInstanceOf[Literal]) =>
-        val hSet = list.map(e => e.eval(null))
+        val hSet = list.map(e => e.eval(EmptyRow))
         InSet(v, HashSet() ++ hSet)
     }
   }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala

@@ -23,7 +23,6 @@ import org.apache.spark.sql.catalyst.analysis._
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.QueryPlan
 import org.apache.spark.sql.catalyst.trees.TreeNode
-import org.apache.spark.sql.catalyst.trees
 
 
 abstract class LogicalPlan extends QueryPlan[LogicalPlan] with Logging {
@@ -277,15 +276,21 @@ abstract class LogicalPlan extends QueryPlan[LogicalPlan] with Logging {
 /**
  * A logical plan node with no children.
  */
-abstract class LeafNode extends LogicalPlan with trees.LeafNode[LogicalPlan] {
+abstract class LeafNode extends LogicalPlan {
   self: Product =>
+
+  override def children: Seq[LogicalPlan] = Nil
 }
 
 /**
  * A logical plan node with single child.
  */
-abstract class UnaryNode extends LogicalPlan with trees.UnaryNode[LogicalPlan] {
+abstract class UnaryNode extends LogicalPlan {
   self: Product =>
+
+  def child: LogicalPlan
+
+  override def children: Seq[LogicalPlan] = child :: Nil
 }
 
 /**

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -452,19 +452,3 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] {
     s"$nodeName(${args.mkString(",")})"
   }
 }
-
-
-/**
- * A [[TreeNode]] with no children.
- */
-trait LeafNode[BaseType <: TreeNode[BaseType]] {
-  def children: Seq[BaseType] = Nil
-}
-
-/**
- * A [[TreeNode]] with a single [[child]].
- */
-trait UnaryNode[BaseType <: TreeNode[BaseType]] {
-  def child: BaseType
-  def children: Seq[BaseType] = child :: Nil
-}