Correctly set bitmask size in from_column_view

python/cudf/cudf/_lib/column.pyx

@@ -155,7 +155,11 @@ cdef class Column:
             )
 
         if value is not None:
-            required_size = bitmask_allocation_size_bytes(self.base_size)
+            # base_size may be zero for a struct column with no
+            # children, but the column may have non-zero length.
+            required_size = bitmask_allocation_size_bytes(
+                max(self.base_size, self._size)
+            )
             if value.size < required_size:
                 error_msg = (
                     "The Buffer for mask is smaller than expected, "
@@ -605,7 +609,9 @@ cdef class Column:
             else:
                 mask = as_buffer(
                     data=mask_ptr,
-                    size=bitmask_allocation_size_bytes(base_size),
+                    size=bitmask_allocation_size_bytes(
+                        max(size+offset, base_size)
+                    ),
                     owner=mask_owner,
                     exposed=True
                 )

python/cudf/cudf/tests/test_struct.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2020-2022, NVIDIA CORPORATION.
+# Copyright (c) 2020-2023, NVIDIA CORPORATION.
 
 import numpy as np
 import pandas as pd
@@ -392,3 +392,13 @@ def test_struct_with_null_memory_usage():
 
     s[2:4] = None
     assert s.memory_usage() == 272
+
+
+@pytest.mark.parametrize("indices", [slice(0, 3), slice(1, 4)])
+def test_struct_empty_children_nulls_slice(indices):
+    values = [None, {}, {}, None]
+
+    s = cudf.Series([None, {}, {}, None])
+    actual = s.iloc[indices]
+    expect = cudf.Series(values[indices], index=range(len(values))[indices])
+    assert_eq(actual, expect)