jayzhan211 commented on PR #13305:
URL: https://github.com/apache/datafusion/pull/13305#issuecomment-2464207671
@sydduckworth Do you remember why `cast should drop input metadata since the
type has changed`
```rust
#[test]
fn test_expr_metadata() {
let mut meta = HashMap::new();
meta.insert("bar".to_string(), "buzz".to_string());
let expr = col("foo");
let schema = MockExprSchema::new()
.with_data_type(DataType::Int32)
.with_metadata(meta.clone());
// col and alias should be metadata-preserving
assert_eq!(meta, expr.metadata(&schema).unwrap());
assert_eq!(meta,
expr.clone().alias("bar").metadata(&schema).unwrap());
// cast should drop input metadata since the type has changed
assert_eq!(
HashMap::new(),
expr.clone()
.cast_to(&DataType::Int64, &schema)
.unwrap()
.metadata(&schema)
.unwrap()
);
let schema = DFSchema::from_unqualified_fields(
vec![Field::new("foo", DataType::Int32,
true).with_metadata(meta.clone())]
.into(),
HashMap::new(),
)
.unwrap();
// verify to_field method populates metadata
assert_eq!(&meta, expr.to_field(&schema).unwrap().1.metadata());
}
```
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