Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21954#discussion_r208272808
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/higherOrderFunctions.scala
---
@@ -0,0 +1,166 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.analysis
+
+import org.apache.spark.sql.catalyst.catalog.SessionCatalog
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.DataType
+
+/**
+ * Resolve a higher order functions from the catalog. This is different
from regular function
+ * resolution because lambda functions can only be resolved after the
function has been resolved;
+ * so we need to resolve higher order function when all children are
either resolved or a lambda
+ * function.
+ */
+case class ResolveHigherOrderFunctions(catalog: SessionCatalog) extends
Rule[LogicalPlan] {
+
+ override def apply(plan: LogicalPlan): LogicalPlan =
plan.resolveOperators {
+ case q: LogicalPlan =>
+ q.transformExpressions {
+ case u @ UnresolvedFunction(fn, children, false)
+ if hasLambdaAndResolvedArguments(children) =>
+ withPosition(u) {
+ catalog.lookupFunction(fn, children) match {
+ case func: HigherOrderFunction => func
+ case other => other.failAnalysis(
+ "A lambda function should only be used in a higher order
function. However, " +
+ s"its class is ${other.getClass.getCanonicalName}, which
is not a " +
+ s"higher order function.")
+ }
+ }
+ }
+ }
+
+ /**
+ * Check if the arguments of a function are either resolved or a lambda
function.
+ */
+ private def hasLambdaAndResolvedArguments(expressions: Seq[Expression]):
Boolean = {
+ val (lambdas, others) =
expressions.partition(_.isInstanceOf[LambdaFunction])
+ lambdas.nonEmpty && others.forall(_.resolved)
+ }
+}
+
+/**
+ * Resolve the lambda variables exposed by a higher order functions.
+ *
+ * This rule works in two steps:
+ * [1]. Bind the anonymous variables exposed by the higher order function
to the lambda function's
+ * arguments; this creates named and typed lambda variables. The
argument names are checked
+ * for duplicates and the number of arguments are checked during this
step.
+ * [2]. Resolve the used lambda variables used in the lambda function's
function expression tree.
+ * Note that we allow the use of variables from outside the current
lambda, this can either
+ * be a lambda function defined in an outer scope, or a attribute in
produced by the plan's
+ * child. If names are duplicate, the name defined in the most inner
scope is used.
+ */
+case class ResolveLambdaVariables(conf: SQLConf) extends Rule[LogicalPlan]
{
+
+ type LambdaVariableMap = Map[String, NamedExpression]
+
+ private val canonicalizer = {
+ if (!conf.caseSensitiveAnalysis) {
+ s: String => s.toLowerCase
+ } else {
+ s: String => s
+ }
+ }
+
+ override def apply(plan: LogicalPlan): LogicalPlan = {
+ plan.resolveOperators {
+ case q: LogicalPlan =>
+ q.mapExpressions(resolve(_, Map.empty))
+ }
+ }
+
+ /**
+ * Create a bound lambda function by binding the arguments of a lambda
function to the given
+ * partial arguments (dataType and nullability only). If the expression
happens to be an already
+ * bound lambda function then we assume it has been bound to the correct
arguments and do
+ * nothing. This function will produce a lambda function with hidden
arguments when it is passed
+ * an arbitrary expression.
+ */
+ private def createLambda(
+ e: Expression,
+ partialArguments: Seq[(DataType, Boolean)]): LambdaFunction = e
match {
--- End diff --
why call it "partial"?
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