dartkron opened a new pull request, #50607:
URL: https://github.com/apache/arrow/pull/50607
### Rationale for this change
`ViewDataImpl` skipped input layout entries marked `ALWAYS_NULL`. A nested
`NullType` has no physical buffer, but its `ArrayData` still carries the
length
and offset needed for the output. Losing this metadata could make a cast
to the
same nested type produce an invalid child array.
Fixes #43838.
### What changes are included in this PR?
Preserve length and offset when matching an input `NullType` with an output
`NullType`, while retaining the previous behavior for other `ALWAYS_NULL`
layouts, including union and run-end encoded types. Add a regression test
for
a sliced nested `NullArray`.
### Are these changes tested?
Yes. The regression test and all 51 CTest targets enabled in the local C++
build pass in an Ubuntu 24.04 container.
### Are there any user-facing changes?
Yes. Casts containing nested `NullType` fields no longer produce invalid
child
arrays. There are no public API changes.
### AI assistance
AI assistance was used during investigation, implementation, and review. I
reviewed the final changes and verified them with the tests described
above.
**This PR contains a "Critical Fix".** The previous behavior could produce
an
invalid array from valid input.
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