[ARROW-15846] [Format] Clarify presence of Struct array validity bitmap

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 8.0.0
• Component/s: Format
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/31285
• Assignee: Antoine Pitrou
• Reporter: Antoine Pitrou
• Created: 04/Mar/22 14:08
• Updated: 11/Jan/23 11:40
• Resolved: 14/Mar/22 16:01

Description

The following wording in the format spec is a bit ambiguous:

A struct array must still have an allocated validity bitmap, if it has one or more null values.

https://arrow.apache.org/docs/format/Columnar.html#struct-layout

This can be misinterpreted as meaning that a struct array with no nulls does not have any buffer at all. In reality, it has an "absent" validity buffer (e.g. with 0 length).

Issue Links

• links to: GitHub Pull Request #12599