cxzl25 opened a new pull request, #2638:
URL: https://github.com/apache/orc/pull/2638
### What changes were proposed in this pull request?
Add a `batchSize > 0` guard in `ConvertTreeReader.convertVector()` before
accessing index 0.
### Why are the changes needed?
When reading an ORC file with schema evolution converting `array<int>` to
`array<string>`, an `ArrayIndexOutOfBoundsException` is thrown if the first
batch processed by the element reader has `childCount=0` (i.e., all rows in the
batch contain empty arrays).
```java
java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at
org.apache.orc.impl.ConvertTreeReaderFactory$StringGroupFromAnyIntegerTreeReader.setConvertVectorElement(ConvertTreeReaderFactory.java:1094)
at
org.apache.orc.impl.ConvertTreeReaderFactory$ConvertTreeReader.convertVector(ConvertTreeReaderFactory.java:305)
at
org.apache.orc.impl.ConvertTreeReaderFactory$StringGroupFromAnyIntegerTreeReader.nextVector(ConvertTreeReaderFactory.java:1115)
at
org.apache.orc.impl.TreeReaderFactory$ListTreeReader.nextVector(TreeReaderFactory.java:2892)
at
org.apache.orc.impl.reader.tree.StructBatchReader.readBatchColumn(StructBatchReader.java:66)
at
org.apache.orc.impl.reader.tree.StructBatchReader.nextBatchForLevel(StructBatchReader.java:101)
at
org.apache.orc.impl.reader.tree.StructBatchReader.nextBatch(StructBatchReader.java:78)
at
org.apache.orc.impl.RecordReaderImpl.nextBatch(RecordReaderImpl.java:1444)
```
### How was this patch tested?
Added `testIntArrayToStringArrayFirstBatchAllEmpty` in
`TestConvertTreeReaderFactory`
### Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude
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