alamb commented on code in PR #7596:
URL: https://github.com/apache/arrow-rs/pull/7596#discussion_r2132466026


##########
arrow-array/src/array/struct_array.rs:
##########
@@ -852,6 +855,67 @@ mod tests {
         assert!(sliced_c1.is_null(2));
     }
 
+    #[test]
+    fn test_struct_array_data_slice() {
+        let x = Int32Array::from(vec![Some(0), Some(1), Some(2), Some(3), 
None, Some(5)]);
+        let struct_array = StructArray::new(
+            Fields::from(vec![Field::new("x", DataType::Int32, true)]),
+            vec![Arc::new(x.clone())],
+            Some(NullBuffer::from(vec![true, true, true, false, true, true])),
+        )
+        .into_data();
+        let sliced = struct_array.slice(1, 4);
+
+        let arr = make_array(sliced);
+        assert_eq!(
+            arr.as_struct().column(0).as_primitive::<Int32Type>(),
+            &x.slice(1, 4)
+        );
+
+        // This next test case is a regression test of a bug detected when 
converting a sliced
+        // struct from C++
+        //
+        // In arrow-rs struct slicing is done by setting the offset and length 
of
+        // child arrays.
+        //
+        // In the C++ implementation of Arrow struct slicing is done by 
setting the offset
+        // and length of the struct array.
+        //
+        // arrow-rs should be able to parse data received from C++ correctly.
+        let x = Int32Array::from(vec![Some(0), Some(1), Some(2), Some(3), 
None, Some(5)]);
+        let y = Int32Array::from(vec![Some(5), Some(6), None, Some(8), 
Some(9), Some(10)]);
+        let struct_array = StructArray::new(
+            Fields::from(vec![
+                Field::new("x", DataType::Int32, true),
+                Field::new("y", DataType::Int32, true),
+            ]),
+            vec![Arc::new(x), Arc::new(y)],
+            Some(NullBuffer::from(vec![true, true, true, false, true, true])),
+        );
+        let struct_array = StructArray::new(
+            Fields::from(vec![Field::new(
+                "inner",
+                struct_array.data_type().clone(),
+                true,
+            )]),
+            vec![Arc::new(struct_array)],
+            Some(NullBuffer::from(vec![true, false, true, true, true, true])),
+        );
+
+        let cpp_sliced_array = make_array(

Review Comment:
   I wonder if there is some way to add a reproducer with actual data that came 
from C/C++. I am not sure how to verify that this reproducer accurately 
reflects the C/C++ code (not that I doubt you, I just don't know how to double 
check it)
   
   Maybe we can add something to 
https://github.com/apache/arrow-testing/tree/master/data? 
   
   Or does it only happen when passing across IPC boundaries? If so maybe we 
can add a test to the integration tests?



##########
arrow-array/src/array/struct_array.rs:
##########
@@ -852,6 +855,67 @@ mod tests {
         assert!(sliced_c1.is_null(2));
     }
 
+    #[test]
+    fn test_struct_array_data_slice() {

Review Comment:
   I did verify that this test fails without the change in this PR
   
   ```
   
   assertion failed: (offset + length) <= self.len()
   thread 'array::struct_array::tests::test_struct_array_data_slice' panicked 
at arrow-data/src/data.rs:550:9:
   assertion failed: (offset + length) <= self.len()
   ```



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