fix(io): keep null lists of structs when projecting Arrow data

pyiceberg/io/pyarrow.py

@@ -2097,7 +2097,15 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
             if isinstance(value_array, pa.StructArray):
                 # This can be removed once this has been fixed:
                 # https://github.com/apache/arrow/issues/38809
-                list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
+                # Keep the validity and offsets buffers of the original array, otherwise null lists become empty lists
+                list_array = pa.Array.from_buffers(
+                    list_initializer(value_array.type),
+                    len(list_array),
+                    list_array.buffers()[:2],
+                    list_array.null_count,
+                    list_array.offset,
+                    [value_array],
+                )
             value_array = self._cast_if_needed(list_type.element_field, value_array)
             arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
             return list_array.cast(arrow_field)

tests/integration/test_reads.py

@@ -1001,10 +1001,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
     arrow_table = table_test_empty_list_and_map.scan().to_arrow()
     assert arrow_table["col_list"].to_pylist() == [None, []]
     assert arrow_table["col_map"].to_pylist() == [None, []]
-    # This should be:
-    # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
-    # Once https://github.com/apache/arrow/issues/38809 has been fixed
-    assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
+    assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]
 
 
 @pytest.mark.integration

tests/io/test_pyarrow.py

@@ -21,7 +21,7 @@
 import tempfile
 import uuid
 import warnings
-from collections.abc import Iterator
+from collections.abc import Callable, Iterator
 from datetime import date, datetime, timezone
 from pathlib import Path
 from typing import Any
@@ -3272,6 +3272,41 @@ def test__to_requested_schema_float_promotion(
     assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]
 
 
+@pytest.mark.parametrize("list_type", [pa.list_, pa.large_list])
+def test__to_requested_schema_null_list_of_structs(list_type: Callable[[pa.DataType], pa.DataType]) -> None:
+    requested_schema = Schema(
+        NestedField(
+            1,
+            "col_list_with_struct",
+            ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
+            required=False,
+        ),
+        NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
+    )
+    arrow_schema = pa.schema(
+        [
+            pa.field("col_list_with_struct", list_type(pa.struct([pa.field("test", pa.int32())]))),
+            pa.field("col_list", list_type(pa.int32())),
+        ]
+    )
+    batch = pa.RecordBatch.from_arrays(
+        [
+            pa.array([[{"test": 1}], [], None, [{"test": 2}, None]], type=arrow_schema.field(0).type),
+            pa.array([[1], [], None, [2, None]], type=arrow_schema.field(1).type),
+        ],
+        schema=arrow_schema,
+    )
+
+    result = _to_requested_schema(requested_schema, requested_schema, batch)
+    assert result.column(0).to_pylist() == [[{"test": 1}], [], None, [{"test": 2}, None]]
+    assert result.column(1).to_pylist() == [[1], [], None, [2, None]]
+
+    # A sliced batch has to keep the nulls as well
+    result = _to_requested_schema(requested_schema, requested_schema, batch.slice(1, 3))
+    assert result.column(0).to_pylist() == [[], None, [{"test": 2}, None]]
+    assert result.column(1).to_pylist() == [[], None, [2, None]]
+
+
 def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
     # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
     # becomes available for `resolve_s3_region`