Fix astype/fillna not maintaining column subclass and types

python/cudf/cudf/core/column_accessor.py

@@ -157,13 +157,17 @@ def _create_unsafe(
         data: Dict[Any, ColumnBase],
         multiindex: bool = False,
         level_names=None,
+        rangeindex: bool = False,
+        label_dtype: Dtype | None = None,
     ) -> ColumnAccessor:
         # create a ColumnAccessor without verifying column
         # type or size
         obj = cls()
         obj._data = data
         obj.multiindex = multiindex
         obj._level_names = level_names
+        obj.rangeindex = rangeindex
+        obj.label_dtype = label_dtype
         return obj
 
     def __iter__(self):

python/cudf/cudf/core/frame.py

@@ -280,6 +280,8 @@ def astype(self, dtype, copy=False, **kwargs):
             data=result_data,
             multiindex=self._data.multiindex,
             level_names=self._data.level_names,
+            rangeindex=self._data.rangeindex,
+            label_dtype=self._data.label_dtype,
         )
 
     @_cudf_nvtx_annotate
@@ -876,6 +878,8 @@ def fillna(
                     data=filled_data,
                     multiindex=self._data.multiindex,
                     level_names=self._data.level_names,
+                    rangeindex=self._data.rangeindex,
+                    label_dtype=self._data.label_dtype,
                 )
             ),
             inplace=inplace,

python/cudf/cudf/tests/test_dataframe.py

@@ -4643,6 +4643,36 @@ def test_dataframe_columns_empty_data_preserves_dtype(dtype, idx_data, data):
     assert_eq(result, expected)
 
 
+@pytest.mark.parametrize("dtype", ["int64", "datetime64[ns]", "int8"])
+def test_dataframe_astype_preserves_column_dtype(dtype):
+    result = cudf.DataFrame([1], columns=cudf.Index([1], dtype=dtype))
+    result = result.astype(np.int32).columns
+    expected = pd.Index([1], dtype=dtype)
+    assert_eq(result, expected)
+
+
+def test_dataframe_astype_preserves_column_rangeindex():
+    result = cudf.DataFrame([1], columns=range(1))
+    result = result.astype(np.int32).columns
+    expected = pd.RangeIndex(1)
+    assert_eq(result, expected)
+
+
+@pytest.mark.parametrize("dtype", ["int64", "datetime64[ns]", "int8"])
+def test_dataframe_fillna_preserves_column_dtype(dtype):
+    result = cudf.DataFrame([1, None], columns=cudf.Index([1], dtype=dtype))
+    result = result.fillna(2).columns
+    expected = pd.Index([1], dtype=dtype)
+    assert_eq(result, expected)
+
+
+def test_dataframe_fillna_preserves_column_rangeindex():
+    result = cudf.DataFrame([1, None], columns=range(1))
+    result = result.fillna(2).columns
+    expected = pd.RangeIndex(1)
+    assert_eq(result, expected)
+
+
 @pytest.mark.parametrize(
     "data",
     [