[Java] Nullability of struct child vectors not preserved in TransferPair

[FiV0]

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

When copying a struct vector via a transfer pair the nullability of the children is not preserved

  @Test
  public void testMakeTransferPairPreserveNullability() {
    Field intField = new Field("int", FieldType.notNullable(MinorType.INT.getType()), null);
    Field structField = new Field("struct", FieldType.notNullable(Struct.INSTANCE), List.of(intField));
    FieldVector vec = structField.createVector(allocator);

    TransferPair tp = vec.getTransferPair(new Field("struct", FieldType.nullable(Struct.INSTANCE), List.of(intField)), allocator);
    tp.transfer();

    FieldVector res = (FieldVector) tp.getTo();

    // passes
    assertEquals(intField, vec.getField().getChildren().get(0));
    // fails
    assertEquals(intField, res.getField().getChildren().get(0));
  }

results in the failure

Expected :int: Int(32, true) not null
Actual   :int: Int(32, true)

Component(s)

Java

[tlm365]

Field structField = new Field("struct", FieldType.notNullable(Struct.INSTANCE), List.of(intField));
FieldVector vec = structField.createVector(allocator);

TransferPair tp = vec.getTransf>erPair(new Field("struct", FieldType.nullable(Struct.INSTANCE), List.of(intField)), allocator);

@FiV0 I don't think it's a bug. The bolding texts above are mismatched and that's the reason for the diff between vec and res.

[vibhatha]

@tlm365 could you explain

The bolding texts above are mismatched

[tlm365]

@vibhatha the Field he passed when create vec is notNullable:
Field structField = new Field("struct", FieldType.notNullable(Struct.INSTANCE), List.of(intField));
FieldVector vec = structField.createVector(allocator);

but nullable when pass to getTransferPair:
TransferPair tp = vec.getTransferPair(new Field("struct", FieldType.nullable(Struct.INSTANCE), List.of(intField)), allocator);

[vibhatha]

@vibhatha the Field he passed when create vec is notNullable: Field structField = new Field("struct", FieldType.notNullable(Struct.INSTANCE), List.of(intField)); FieldVector vec = structField.createVector(allocator);

but nullable when pass to getTransferPair: TransferPair tp = vec.getTransferPair(new Field("struct", FieldType.nullable(Struct.INSTANCE), List.of(intField)), allocator);

Oh I didn't catch that. Thanks @tlm365

[FiV0]

This is about the nullability of the the child and not the struct. Why should the nullability of a struct affect the nullability of its children?

[vibhatha]

Hmm, @FiV0 I agree. I also tested it even with adding matching nullability, just for the sake of the argument. But still the issue is there.

[vibhatha]

I am taking a look at this.

[vibhatha]

I think the issue is here addVectorAsNullable field is not properly set. This doesn't go to the buffer transfer level, from the type setting level, the nullability is inaccurately set AFAIU from debugging.

[vibhatha]

I will make a draft PR shortly.

[lidavidm]

Issue resolved by pull request 41785
#41785