pitrou commented on code in PR #46408:
URL: https://github.com/apache/arrow/pull/46408#discussion_r2109183910
##########
cpp/src/arrow/ipc/read_write_test.cc:
##########
@@ -579,6 +579,40 @@ TEST_F(TestIpcRoundTrip, SpecificMetadataVersion) {
TestMetadataVersion(MetadataVersion::V5);
}
+TEST_F(TestIpcRoundTrip, AlienSlice) {
+ // This tests serialization of a sliced ListArray that got sliced "the Rust
+ // way": by slicing the value_offsets buffer, but keeping top-level offset at
+ // 0.
+
+ // Values buffer [1, 2, 3, 4, 5]
+ TypedBufferBuilder<int32_t> values_builder;
+ ASSERT_OK(values_builder.Reserve(5));
+ for (int32_t i = 1; i <= 5; i++) {
+ ASSERT_OK(values_builder.Append(i));
+ }
+ ASSERT_OK_AND_ASSIGN(auto values_buffer, values_builder.Finish());
Review Comment:
Note that this could be written more succinctly:
```c++
// Values array
auto child_data = ArrayFromJSON(int32(), "[1, 2, 3, 4, 5]")->data();
```
##########
cpp/src/arrow/ipc/writer.cc:
##########
@@ -327,11 +327,9 @@ class RecordBatchSerializer {
auto offsets = array.value_offsets();
int64_t required_bytes = sizeof(offset_type) * (array.length() + 1);
- if (array.offset() != 0) {
- // If we have a non-zero offset, then the value offsets do not start at
- // zero. We must a) create a new offsets array with shifted offsets and
- // b) slice the values array accordingly
-
+ if (array.offset() != 0 || (array.length() > 0 && array.value_offset(0) >
0)) {
Review Comment:
> This path is extensively tested by TestFeather.SliceStringsRoundTrip.
It would be nice to add a similar test for list slices, however. This can
probably be in the same `TestFeather` fixture.
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