brucearctor opened a new pull request, #69938:
URL: https://github.com/apache/doris/pull/69938
### What problem does this PR solve?
Issue Number: close #69930
Related PR: N/A
Problem Summary:
When an enclosing higher-order function (such as `ARRAY_FIRST(p ->
STRUCT_ELEMENT(p, 1) = k, arr)`) references slots from both sides of a join, it
cannot be pushed down as a whole. `PushDownProject` then descends into its
children via `rewriteDownShortCircuit`.
Because `Expression.getInputSlots()` (`Expression.java:73-74`) deliberately
excludes `ArrayItemSlot`, a `PreferPushDownProject` sub-expression inside the
lambda body that only references the lambda parameter `p` (such as
`element_at(p, 1)`) has an empty `getInputSlots()` set. Both
`PushDownProject.pushDownProjectInExpressions` and
`PushdownProjectHelper.pushDownExpression` treat
`child.getOutputSet().containsAll(emptySet)` as satisfied by the first child
(`join.left()`) and extract `element_at(p, 1)` out of its enclosing `Lambda`
into a child `LogicalProject`, leaving `p` unbound:
**Before:**
```text
LogicalProject(k, element_at(element_at(array_filter(arr, array_map(p -> #x
= k, arr)), 1), 2) AS v)
LogicalJoin(CROSS_JOIN)
left: LogicalProject(k, element_at(p, 1) AS #x) <-- 'p'
(ArrayItemSlot) is unbound here!
LogicalOneRowRelation(k)
right: LogicalOneRowRelation(arr)
```
During physical plan translation
(`PhysicalPlanTranslator.visitPhysicalProject` ->
`ExpressionTranslator.visitArrayItemSlot`), `p` is not present in
`lambdaSlotToColumnRef` (which is only populated while translating
`visitArrayMap`), returning `null` and failing with a `NullPointerException` in
`Expr.extractSlots`.
**After:**
```text
LogicalProject(k, element_at(element_at(array_filter(arr, array_map(p ->
element_at(p, 1) = k, arr)), 1), 2) AS v)
LogicalJoin(CROSS_JOIN)
left: LogicalOneRowRelation(k)
right: LogicalOneRowRelation(arr)
```
**Fix:**
- Guard both `PreferPushDownProject` rewrite sites in `PushDownProject`
(`pushDownProjectInExpressions` and `PushdownProjectHelper.pushDownExpression`)
with `!hasFreeLambdaArgument(e)`.
- `hasFreeLambdaArgument` uses an O(1) `containsType(ArrayItemSlot.class)`
fast path and tracks bound lambda parameter `ExprId`s lexically across nested
`Lambda`s (checking `ArrayItemReference.getArrayExpression()` in the outer
scope before binding the lambda's own parameters).
- Complete, self-contained higher-order expressions whose relational inputs
come from a single child continue to be pushed down as before.
cc @matanper @morrySnow @924060929 @englefly
### Release note
None
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [x] Unit Test (`PushDownProjectTest`)
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [x] No.
- [ ] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [x] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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