GH-37004: [C++][Python] Fix dropped child data when viewing/casting e… - #50502
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pitrou merged 1 commit intoJul 22, 2026
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…ting extension types with nested storage
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July 14, 2026 19:14
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For the record, I wouldn't call this a critical fix, more of a regular bug, but the boundary can be a bit fuzzy. |
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This PR looks good to me. Thank you @connorsimms !
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After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit 450b793. There were no benchmark performance regressions. 🎉 The full Conbench report has more details. It also includes information about 6 possible false positives for unstable benchmarks that are known to sometimes produce them. |
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Rationale for this change
table.cast(table.schema)errored or segfaulted when the schema contained a struct with an extension-typed field whose storage is a list.This cast takes a zero-copy view, and
ViewDataImpl::MakeDataViewfound children usingtype->fields(), which is never populated for extension types since their structure is instorage_type(). The same issue exists inAccumulateLayouts. The storage's child data gets dropped and leaves an invalid array that downstream code throws/crashes on.This bug is similar to #37669, except that the fix for #37669 addressed casting to an extension with nested storage but not this particular struct-wrapped view path.
What changes are included in this PR?
cpp/src/arrow/array/data.cc-AccumulateLayoutsandViewDataImpl::MakeDataViewnow recurse intostorage_type()->fields()forExtensionType, instead of the extension type's emptyfields().cpp/src/arrow/array/array_view_test.ccpython/pyarrow/tests/test_extension_type.pyAre these changes tested?
Yes,
cpp/src/arrow/array/array_view_test.cc- Two tests for viewing an extension array with nested storage for fixed-size and variable-size lists.python/pyarrow/tests/test_extension_type.py- A test casting a table / struct containing an extension type with list-based storage to its own schema.Are there any user-facing changes?
No API changes. Operations that previously raised errors or crashed relating to casting/viewing a struct or table with an extension type with nested storage now succeed.