Describe the bug, including details regarding any error messages, version, and platform.

I cannot create a StructVector with a dense-union child - it fails with the following stack trace:

java.lang.UnsupportedOperationException: Unknown type: DENSEUNION
	at org.apache.arrow.vector.complex.impl.NullableStructWriter.<init>(NullableStructWriter.java:258)
	at org.apache.arrow.vector.complex.StructVector.<init>(StructVector.java:69)
	at xtdb.vector.StructVectorWriterTest.struct with DUV child(StructVectorWriterTest.kt:101)

Test code is essentially:

Field child = new Field("child", FieldType.notNullable(new ArrowType.Union(UnionMode.Dense, null)), emptyList());
Field struct = new Field("foo", FieldType.notNullable(ArrowType.Struct.INSTANCE), List.of(child));

try(RootAllocator allocator = new RootAllocator();
   StructVector structVec = new StructVector(struct, allocator, null)) {
            
   System.out.println("working!");
}

I suspect it's a case of adding DENSEUNION to the switch in the NullableStructWriter constructor, with a similar implementation to the sparse UNION?

Cheers,

James

Component(s)

Java