[v25.3.x] iceberg: don't reject new fields with required descendants#30591
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nvartolomei merged 1 commit intoMay 22, 2026
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validate_schema_transform incorrectly rejected adding a new optional column whose nested type contains structurally-required descendants (e.g. an optional map, whose keys are always required). The walk visited every annotated field and triggered new_required_field on the nested required key/element. Stop descending into a subtree once an is_new ancestor is encountered: the substructure is part of the new type's definition, not a separate top-level addition. The same reasoning applies to required list elements and required struct subfields, though in practice only the map-key case arises today. The datalake record translator coerces all incoming schema fields to optional (see record_translator.cc), leaving map keys as the only structurally-required descendants. The list and struct cases are covered by regression tests for completeness. (cherry picked from commit 07afd25)
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CI test resultstest results on build#84887
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Backport of PR #30585
Conflict details
validate_schema_transformon v25.3.x still used thefor_each_field-with-lambda traversal; the PR replaces it with a stack-based walk that stops descending once anis_newancestor is reached. Took the incoming side verbatim (helperschunked_vectorandreverse_field_collecting_visitorare already available via the existingcompatibility_utils.hinclude), preserving the intended bug fix.