liamzwbao commented on code in PR #9338:
URL: https://github.com/apache/arrow-rs/pull/9338#discussion_r2761791785
##########
arrow-string/src/regexp.rs:
##########
@@ -180,7 +180,6 @@ pub fn regexp_is_match_scalar<'a, S>(
where
&'a S: StringArrayType<'a>,
{
- let null_bit_buffer = array.nulls().map(|x| x.inner().sliced());
Review Comment:
We don't have `.sliced()` unfortunately, but we could rebuild the
`NullBuffer`
##########
arrow-string/src/substring.rs:
##########
@@ -360,24 +345,29 @@ fn fixed_size_binary_substring(
})
.for_each(|(start, end)|
new_values.extend_from_slice(&data[start..end]));
- let array_data = unsafe {
- ArrayData::new_unchecked(
- DataType::FixedSizeBinary(new_len),
- num_of_elements,
- None,
- array.nulls().map(|b| b.inner().sliced()),
- 0,
- vec![new_values.into()],
- vec![],
- )
+ let nulls = if new_len == 0 {
+ // FixedSizeBinaryArray::new takes length from the values buffer,
except when size == 0.
+ // In that case it uses the null buffer length, so preserve the
original length here.
+ // Example: ["", "", ""] -> substring(..., 1, Some(2)) should keep
len=3;
+ // otherwise it collapses to an empty array (len=0).
+ array
+ .nulls()
+ .cloned()
+ .or_else(|| Some(NullBuffer::new_valid(num_of_elements)))
Review Comment:
That's mainly because `FixedSizeBinaryArray::new` treats `size == 0`
specially: if both `values` and `nulls` are `None`, it infers `len = 0`.
https://github.com/apache/arrow-rs/blob/7291147175a11a4748d9ea5a06ea42807bf36e3c/arrow-array/src/array/fixed_size_binary_array.rs#L97-L105
In `substring::tests::without_nulls_fixed_size_binary`, some cases produce
size‑0 substrings, and without this change the result collapses to an empty
array and fail the tests. Providing a `nulls` buffer here simply preserves the
expected length to produce correct results (e.g., `["", "", ""]`).
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