JoshElkind opened a new pull request, #20281:
URL: https://github.com/apache/datafusion/pull/20281

   ## Which issue does this PR close?
   
   - Closes #15847.
   
   ## Rationale for this change
   
   As a follow-on to #15646 (Extension Type / Metadata support for Scalar 
UDFs), the narrow helpers on ExprSchema and ExprSchemable can be deprecated in 
favor of the single “get the field” API. Callers should use field_from_column / 
to_field and then read type, nullability, and metadata from the returned field, 
giving one consistent way to resolve expression/column schema info and allowing 
the deprecated methods to be removed in a later release.
   
   ## What changes are included in this PR?
   
   ExprSchema (datafusion_common): Deprecate nullable(col), data_type(col), 
metadata(col), and data_type_and_nullable(col) with #[deprecated(since = 
"53.0.0", note = "use field_from_column")]. Default implementations delegate to 
field_from_column(col). ExprSchemable (datafusion_expr): Deprecate 
get_type(schema), nullable(schema), and metadata(schema) with 
#[deprecated(since = "53.0.0", note = "use to_field")]; data_type_and_nullable 
was already deprecated (since 51.0.0). Default implementations delegate to 
to_field(schema). All internal uses of these methods are updated to to_field / 
field_from_column across expr, optimizer, sql, spark, substrait, examples, and 
docs. Test fixes (no production logic changed): test_inlist_nullability “long 
list” case now uses 7 elements so it hits the list.len() > 6 path; 
test_like_nullability expects nullable for Like/SimilarTo (current 
implementation always returns nullable); rewrite_sort_cols_by_agg_alias 
expected values use Column::new_unqualif
 ied so they match the rewriter’s unqualified output column names. Clippy: 
addressed collapsible_if and added #[expect(deprecated)] for the Expr::Wildcard 
match arm in expr_schema.rs.
   
   ## Are these changes tested?
   
   Yes. Existing tests cover the behavior; no new tests were added. The three 
test updates only align expectations with current implementation. cargo test -p 
datafusion-expr --lib and the broader test suite pass. Deprecated methods keep 
default implementations so behavior is unchanged for any remaining external 
callers until they migrate.
   
   ## Are there any user-facing changes?
   
   Yes. ExprSchema methods data_type, nullable, metadata, 
data_type_and_nullable are deprecated in favor of field_from_column(col) then 
the field’s accessors. ExprSchemable methods get_type, nullable, metadata, 
data_type_and_nullable are deprecated in favor of to_field(schema) then the 
field’s .data_type(), .is_nullable(), .metadata(). This is deprecation only; no 
APIs are removed and behavior is unchanged. The user guide 
(working-with-exprs.md) already documents using to_field for expression 
type/nullability.


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