BUG: Fix cast_pointwise_result with all-NA values

doc/source/whatsnew/v3.0.0.rst

@@ -942,6 +942,7 @@ Numeric
 
 Conversion
 ^^^^^^^^^^
+- Bug in :meth:`BaseMaskedArray._cast_pointwise_result` with all-NA values results returned ``object`` dtype instead of preserving the original dtype (:issue:`62344`)
 - Bug in :meth:`DataFrame.astype` not casting ``values`` for Arrow-based dictionary dtype correctly (:issue:`58479`)
 - Bug in :meth:`DataFrame.update` bool dtype being converted to object (:issue:`55509`)
 - Bug in :meth:`Series.astype` might modify read-only array inplace when casting to a string dtype (:issue:`57212`)

pandas/core/arrays/masked.py

@@ -149,6 +149,8 @@ def _from_sequence(cls, scalars, *, dtype=None, copy: bool = False) -> Self:
         return cls(values, mask)
 
     def _cast_pointwise_result(self, values) -> ArrayLike:
+        if isna(values).all():
+            return type(self)._from_sequence(values, dtype=self.dtype)
         values = np.asarray(values, dtype=object)
         result = lib.maybe_convert_objects(values, convert_to_nullable_dtype=True)
         lkind = self.dtype.kind

pandas/tests/extension/test_masked.py

@@ -362,7 +362,21 @@ def check_accumulate(self, ser: pd.Series, op_name: str, skipna: bool):
         tm.assert_series_equal(result, expected)
 
     def test_loc_setitem_with_expansion_preserves_ea_index_dtype(self, data, request):
-        if data.dtype.kind == "b":
-            mark = pytest.mark.xfail(reason="GH#62344 incorrectly casts to object")
-            request.applymarker(mark)
         super().test_loc_setitem_with_expansion_preserves_ea_index_dtype(data)
+
+    @pytest.mark.parametrize(
+        "arr, values",
+        [
+            (pd.array([True, False]), [pd.NA, pd.NA]),
+            (pd.array([1, 2]), [pd.NA, pd.NA]),
+        ],
+    )
+    def test_cast_pointwise_result_all_na_respects_dtype(self, arr, values):
+        """
+        GH#62344
+        Ensure that _cast_pointwise_result respects the original dtype
+        even when the result consists entirely of NA values.
+        """
+        result = arr._cast_pointwise_result(values)
+        assert result.dtype == arr.dtype
+        assert all(x is pd.NA for x in result)