peter-toth commented on code in PR #38034:
URL: https://github.com/apache/spark/pull/38034#discussion_r1071351771
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala:
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@@ -618,6 +618,212 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]]
extends Product with Tre
}
}
+ /**
+ * Returns alternative copies of this node where `rule` has been recursively
applied to the tree.
+ *
+ * Users should not expect a specific directionality. If a specific
directionality is needed,
+ * multiTransformDownWithPruning or multiTransformUpWithPruning should be
used.
+ *
+ * @param rule a function used to generate transformed alternatives for a
node
+ * @return the stream of alternatives
+ */
+ def multiTransformDown(
+ rule: PartialFunction[BaseType, Stream[BaseType]]): Stream[BaseType] = {
+ multiTransformDownWithPruning(AlwaysProcess.fn, UnknownRuleId)(rule)
+ }
+
+ /**
+ * Returns alternative copies of this node where `rule` has been recursively
applied to the tree.
+ *
+ * Users should not expect a specific directionality. If a specific
directionality is needed,
+ * multiTransformDownWithPruning or multiTransformUpWithPruning should be
used.
+ *
+ * @param rule a function used to generate transformed alternatives for a
node and the
+ * `autoContinue` flag
+ * @return the stream of alternatives
+ */
+ def multiTransformDownWithContinuation(
+ rule: PartialFunction[BaseType, (Stream[BaseType], Boolean)]):
Stream[BaseType] = {
+ multiTransformDownWithContinuationAndPruning(AlwaysProcess.fn,
UnknownRuleId)(rule)
+ }
+
+ /**
+ * Returns alternative copies of this node where `rule` has been recursively
applied to the tree.
+ *
+ * Users should not expect a specific directionality. If a specific
directionality is needed,
+ * multiTransformDownWithPruning or multiTransformUpWithPruning should be
used.
+ *
+ * @param rule a function used to generate transformed alternatives for a
node
+ * @param cond a Lambda expression to prune tree traversals. If
`cond.apply` returns false
+ * on a TreeNode T, skips processing T and its subtree;
otherwise, processes
+ * T and its subtree recursively.
+ * @param ruleId is a unique Id for `rule` to prune unnecessary tree
traversals. When it is
+ * UnknownRuleId, no pruning happens. Otherwise, if `rule`
(with id `ruleId`)
+ * has been marked as in effective on a TreeNode T, skips
processing T and its
+ * subtree. Do not pass it if the rule is not purely
functional and reads a
+ * varying initial state for different invocations.
+ * @return the stream of alternatives
+ */
+ def multiTransformDownWithPruning(
+ cond: TreePatternBits => Boolean,
+ ruleId: RuleId = UnknownRuleId
+ )(rule: PartialFunction[BaseType, Stream[BaseType]]): Stream[BaseType] = {
+ multiTransformDownWithContinuationAndPruning(cond, ruleId)(rule.andThen(_
-> false))
+ }
+
+ /**
+ * Returns alternative copies of this node where `rule` has been recursively
applied to it and all
+ * of its children (pre-order).
+ *
+ * As it is very easy to generate enormous number of alternatives when the
input tree is huge or
+ * when the rule returns large number of alternatives, this function returns
the alternatives as a
+ * lazy `Stream` to be able to limit the number of alternatives generated at
the caller side as
+ * needed.
+ *
+ * The rule should not apply to indicate that the original node without any
transformation is a
+ * valid alternative.
+ *
+ * The rule can return `Stream.empty` to indicate that the original node
should be pruned. In this
+ * case `multiTransform` returns an empty `Stream`.
+ *
+ * Please consider the following examples of `input.multiTransform(rule)`:
+ *
+ * We have an input expression:
+ * `Add(a, b)`
+ *
+ * 1.
+ * We have a simple rule:
+ * `a` => `Stream(1, 2)`
+ * `b` => `Stream(10, 20)`
+ * `Add(a, b)` => `Stream(11, 12, 21, 22)`
+ *
+ * The output is:
+ * `Stream(11, 12, 21, 22)`
+ *
+ * 2.
+ * In the previous example if we want to generate alternatives of `a` and
`b` too then we need to
+ * explicitly add the original `Add(a, b)` expression to the rule:
+ * `a` => `Stream(1, 2)`
+ * `b` => `Stream(10, 20)`
+ * `Add(a, b)` => `Stream(11, 12, 21, 22, Add(a, b))`
+ *
+ * The output is:
+ * `Stream(11, 12, 21, 22, Add(1, 10), Add(2, 10), Add(1, 20), Add(2, 20))`
+ *
+ * 3.
+ * It is not always easy to determine if we will do any child expression
mapping but we can enable
+ * the `autoContinue` flag to get the same result:
Review Comment:
Yes, indeed. And I don't have any other use case either, so I will remove
that.
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