Function adjust_offsets_for_slice

datafusion/common/src/utils/mod.rs:1102–1117

If `list` is sliced, returns an adjusted offset buffer so that it points to the sliced portion of the list values, and not the whole list values

(
    list: &GenericListArray<O>,
)

/// If `list` is sliced, returns an adjusted offset buffer so that
/// it points to the sliced portion of the list values, and not the whole list values
pub fn adjust_offsets_for_slice<O: OffsetSizeTrait>(
    list: &GenericListArray<O>,
) -> OffsetBuffer<O> {
    let offsets = list.offsets();

    if let (Some(first), Some(last)) = (offsets.first(), offsets.last())
        && (!first.is_zero() || last.as_usize() != list.values().len())
    {
        let offsets = offsets.iter().map(|offset| *offset - *first).collect();

        //todo: use unsafe Offset::new_unchecked?
        return OffsetBuffer::new(offsets);
    }

    offsets.clone()
}

/// For lists and large lists, truncates the sublist of null values
/// Otherwise returns an error