Refactor cast_with_target_field_and_options

Simplify is_valid_cast logic to compute a single decision.
Return a single not_impl_err! for invalid cast cases.
Construct CastExpr::new_with_target_field(...) once
on the successful path, enhancing code clarity and
reducing duplication.

Author: kosiew

datafusion/physical-expr/src/expressions/cast.rs

@@ -338,34 +338,26 @@ pub(crate) fn cast_with_target_field_and_options(
 ) -> Result<Arc<dyn PhysicalExpr>> {
     let expr_type = expr.data_type(input_schema)?;
     let cast_type = target_field.data_type().clone();
-    if expr_type == cast_type {
-        Ok(Arc::new(CastExpr::new_with_target_field(
-            expr,
-            target_field,
-            cast_options,
-        )))
+    let is_valid_cast = if expr_type == cast_type {
+        true
     } else if matches!((&expr_type, &cast_type), (Struct(_), Struct(_))) {
-        if can_cast_struct_types(&expr_type, &cast_type) {
-            // Allow struct-to-struct casts that pass name-based compatibility validation.
-            // This validation is applied at planning time (now) to fail fast, rather than
-            // deferring errors to execution time. The name-based casting logic will be
-            // executed at runtime via ColumnarValue::cast_to.
-            Ok(Arc::new(CastExpr::new_with_target_field(
-                expr,
-                target_field,
-                cast_options,
-            )))
-        } else {
-            not_impl_err!("Unsupported CAST from {expr_type} to {cast_type}")
-        }
-    } else if can_cast_types(&expr_type, &cast_type) {
+        // Allow struct-to-struct casts that pass name-based compatibility validation.
+        // This validation is applied at planning time (now) to fail fast, rather than
+        // deferring errors to execution time. The name-based casting logic will be
+        // executed at runtime via ColumnarValue::cast_to.
+        can_cast_struct_types(&expr_type, &cast_type)
+    } else {
+        can_cast_types(&expr_type, &cast_type)
+    };
+
+    if !is_valid_cast {
+        not_impl_err!("Unsupported CAST from {expr_type} to {cast_type}")
+    } else {
         Ok(Arc::new(CastExpr::new_with_target_field(
             expr,
             target_field,
             cast_options,
         )))
-    } else {
-        not_impl_err!("Unsupported CAST from {expr_type} to {cast_type}")
     }
 }