bersprockets opened a new pull request #35851:
URL: https://github.com/apache/spark/pull/35851
Backport of #35837.
### What changes were proposed in this pull request?
When building the project list from an aggregate sequence in
`ExtractGenerator`, convert the aggregate sequence to an `IndexedSeq` before
performing the flatMap operation.
### Why are the changes needed?
This query fails with a `NullPointerException`:
```
val df = Seq(1, 2, 3).toDF("v")
df.select(Stream(explode(array(min($"v"), max($"v"))), sum($"v")):
_*).collect
```
If you change `Stream` to `Seq`, then it succeeds.
`ExtractGenerator` uses a flatMap operation over `aggList` for two purposes:
- To produce a new aggregate list
- to update `projectExprs` (which is initialized as an array of nulls).
When `aggList` is a `Stream`, the flatMap operation evaluates lazily, so all
entries in `projectExprs` after the first will still be null when the rule
completes.
Changing `aggList` to an `IndexedSeq` forces the flatMap to evaluate eagerly.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
New unit test
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