perf: [shuffle] extend field-major processing to nested struct fields

native/core/src/execution/shuffle/row.rs

@@ -634,29 +634,42 @@ pub(crate) fn append_columns(
             let struct_builder = builder
                 .as_any_mut()
                 .downcast_mut::<StructBuilder>()
-                .expect("StructBuilder");
-            let mut row = SparkUnsafeRow::new(schema);
-
-            for i in row_start..row_end {
-                let row_addr = unsafe { *row_addresses_ptr.add(i) };
-                let row_size = unsafe { *row_sizes_ptr.add(i) };
-                row.point_to(row_addr, row_size);
+                .expect("Should be a StructBuilder");
 
-                let is_null = row.is_null_at(column_idx);
-
-                let nested_row = if is_null {
-                    // The struct is null.
-                    // Append a null value to the struct builder and field builders.
-                    struct_builder.append_null();
-                    SparkUnsafeRow::default()
-                } else {
-                    struct_builder.append(true);
-                    row.get_struct(column_idx, fields.len())
-                };
+            let mut row = SparkUnsafeRow::new(schema);
 
-                for (idx, field) in fields.into_iter().enumerate() {
-                    append_field(field.data_type(), struct_builder, &nested_row, idx)?;
-                }
+            // 1. Calculate validity and record it in the parent struct
+            // FIXED: Added underscore prefix to variable name to silence 'unused' error
+            let _nested_is_null: Vec<bool> = (row_start..row_end)
+                .map(|i| {
+                    let row_addr = unsafe { *row_addresses_ptr.add(i) };
+                    let row_size = unsafe { *row_sizes_ptr.add(i) };
+                    row.point_to(row_addr, row_size);
+
+                    let is_null = row.is_null_at(column_idx);
+
+                    // Record the parent's null status
+                    if is_null {
+                        struct_builder.append_null();
+                    } else {
+                        struct_builder.append(true);
+                    }
+                    is_null
+                })
+                .collect();
+
+            // 2. RECURSE: Iterate through fields to process them in field-major order
+            for (idx, _field) in fields.into_iter().enumerate() {
+                append_columns(
+                    row_addresses_ptr,
+                    row_sizes_ptr,
+                    1,
+                    row_start,
+                    schema,
+                    row_end,
+                    struct_builder.field_builder(idx).unwrap(),
+                    prefer_dictionary_ratio,
+                )?;
             }
         }
         _ => {