kosiew commented on issue #20164:
URL: https://github.com/apache/datafusion/issues/20164#issuecomment-4028351390
#20814 adds these changes:
Key changes include:
1. **Field-aware CastExpr**
* Replace the `cast_type: DataType` field with `target_field: FieldRef`.
* Add `new_with_target_field` constructor to explicitly construct
field-aware casts.
* Keep the existing `new(expr, DataType)` constructor as a compatibility
shim that creates a canonical field.
2. **Return-field and nullability behavior**
* `return_field` now returns the full `target_field`, preserving name,
nullability, and metadata.
* `nullable()` now derives its result from the resolved target field
rather than the input expression.
* Add compatibility logic for legacy type-only casts to preserve previous
behavior.
3. **Struct cast validation improvements**
* Struct-to-struct casting now validates compatibility using field
information before execution.
* Planning-time validation prevents unsupported casts from reaching
execution.
4. **Shared cast property logic**
* Introduce shared helper functions (`cast_expr_properties`,
`is_order_preserving_cast_family`) for determining ordering preservation.
* Reuse this logic in both `CastExpr` and `CastColumnExpr` to avoid
duplicated implementations.
5. **Schema rewriter improvements**
* Refactor physical column resolution into `resolve_physical_column`.
* Simplify cast insertion logic when logical and physical fields differ.
* Pass explicit physical and logical fields to cast creation for improved
correctness.
6. **Ordering equivalence simplification**
* Introduce `substitute_cast_like_ordering` helper to unify handling of
`CastExpr` and `CastColumnExpr` in ordering equivalence analysis.
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