cloud-fan commented on code in PR #38034:
URL: https://github.com/apache/spark/pull/38034#discussion_r1070212796
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala:
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@@ -618,6 +618,165 @@ 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,
+ * multiTransformDown or multiTransformUp should be used.
+ *
+ * @param rule a function used to generate transformed alternatives for a
node
+ * @return the stream of alternatives
+ */
+ def multiTransform(rule: PartialFunction[BaseType, Seq[BaseType]]):
Stream[BaseType] = {
+ multiTransformDown(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 multiTransformWithPruning(
+ cond: TreePatternBits => Boolean,
+ ruleId: RuleId = UnknownRuleId
+ )(rule: PartialFunction[BaseType, Seq[BaseType]]): Stream[BaseType] = {
+ multiTransformDownWithPruning(cond, ruleId)(rule).map(_._1)
+ }
+
+ /**
+ * Returns alternative copies of this node where `rule` has been recursively
applied to it and all
+ * of its children (pre-order).
+ *
+ * @param rule the function used to generate transformed alternatives for a
node
+ * @return the stream of alternatives
+ */
+ def multiTransformDown(rule: PartialFunction[BaseType, Seq[BaseType]]):
Stream[BaseType] = {
+ multiTransformDownWithPruning(AlwaysProcess.fn,
UnknownRuleId)(rule).map(_._1)
+ }
+
+ /**
+ * 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.
+ *
+ * To indicate that the original node without any transformation is a valid
alternative the rule
+ * can either:
+ * - not apply or
+ * - return an empty `Seq` or
+ * - a `Seq` that contains a node that is equal to the original node.
+ *
+ * Please note that this function always consider the original node as a
valid alternative (even
+ * if the original node is not included in the returned `Seq`) if the rule
can transform any of
+ * the descendants of the node. E.g. consider a simple expression:
+ * `Add(a, b)`
+ * and a rule that returns:
+ * `Seq(1, 2)` for `a` and
+ * `Seq(10, 20)` for `b` and
+ * `Seq(11, 12, 21, 22)` for `Add(a, b)` (note that the original `Add(a,
b)` is not returned)
+ * then the result of `multiTransform` is:
+ * `Seq(11, 12, 21, 22, Add(1, 10), Add(2, 10), Add(1, 20), Add(2, 20))`.
Review Comment:
This is a good example, and explains why we don't have `multiTransformUp`.
Can we highlight this and remove `multiTransform` as callers should be aware
that it's tramsform down?
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