Abhisheklearn12 opened a new pull request, #10510:
URL: https://github.com/apache/arrow-rs/pull/10510
# Which issue does this PR close?
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Split out of #10436 at review request, which is the PR linked to #8985.
# Rationale for this change
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`view_from_dict_values` appends a view for every non-null key without
checking whether the value it points at is null, so a null dictionary value
surfaces as the empty slice its offsets span:
```rust
// values ["aa", NULL, "cc"], keys [0, 1, 2]
cast(&dict, &DataType::Utf8View) // before: ["aa", "", "cc"]
// after: ["aa", null, "cc"]
cast(&dict, &DataType::Utf8) // unchanged: ["aa", null, "cc"]
```
unpack_dictionary goes through take, and impl From<&GenericByteArray> for
GenericByteViewArray branches on is_null, so both already produce null here.
Only the dictionary to view path disagreed.
# What changes are included in this PR?
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Check value validity before appending a view. Also bounds-check the key
before indexing the offsets, turning an out of range key from undefined
behaviour into an InvalidArgumentError.
# Are these changes tested?
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Yes. The new test fails on the unfixed code, giving `Some("")` where `None`
is expected.
# Are there any user-facing changes?
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`Dictionary<_, Utf8>` -> `Utf8View `and `Dictionary<_, Binary> ->
BinaryView` now produce null for a null dictionary value instead of an empty
string.
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