sunchao commented on code in PR #7381:
URL: https://github.com/apache/datafusion-comet/pull/7381#discussion_r4437121055


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native/spark-expr/src/struct_funcs/get_struct_field.rs:
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@@ -123,6 +125,20 @@ impl PhysicalExpr for GetStructField {
     }
 }
 
+/// The scalar that a one-row array holds. A list wraps the array as is: 
`try_from_array` rebuilds
+/// a list's element field from its name and nullability, which drops metadata 
such as a Variant
+/// element's extension type, so the scalar's type would no longer match 
`data_type`.
+fn single_row_scalar(array: ArrayRef) -> DataFusionResult<ScalarValue> {
+    Ok(match array.data_type() {
+        DataType::List(_) => 
ScalarValue::List(Arc::new(array.as_list::<i32>().clone())),
+        DataType::LargeList(_) => 
ScalarValue::LargeList(Arc::new(array.as_list::<i64>().clone())),
+        DataType::FixedSizeList(_, _) => {
+            
ScalarValue::FixedSizeList(Arc::new(array.as_fixed_size_list().clone()))
+        }
+        _ => ScalarValue::try_from_array(&array, 0)?,

Review Comment:
   **Preserve the element field for `ListView` and `LargeListView` too.** I 
evaluated `GetStructField` on a one-row `Literal(Struct)` whose list-view 
element had `ARROW:extension:name` metadata. For both offset widths, 
`expr.data_type()` retained the metadata but `expr.evaluate()` returned a 
scalar without it. The base expression preserved it on the same input. 
DataFusion 55.2 rebuilds these two views in `try_from_array` just as it does 
the other list types. Wrapping their one-row arrays directly and extending the 
existing metadata test to both widths would keep the declared and evaluated 
types consistent. I reproduced this through the native `PhysicalExpr` API. 
Spark’s standard `ArrayType` maps to `List`, and I found no Spark SQL producer 
for this case.



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