BUG: Failure in empty boolean CategoricalIndex

Fixes GH #22702.

Author: pganssle

pandas/core/arrays/categorical.py

@@ -2439,11 +2439,16 @@ def _get_codes_for_values(values, categories):
     """
     utility routine to turn values into codes given the specified categories
     """
-
     from pandas.core.algorithms import _get_data_algo, _hashtables
     if not is_dtype_equal(values.dtype, categories.dtype):
         values = ensure_object(values)
         categories = ensure_object(categories)
+    else:
+        # These may be Index, in which case their dtype would be coerced
+        # as part of _get_data_algo; in that case, we should retrieve the
+        # underlying numpy array instead.
+        values = getattr(values, 'values', values)
+        categories = getattr(categories, 'values', categories)
 
     (hash_klass, vec_klass), vals = _get_data_algo(values, _hashtables)
     (_, _), cats = _get_data_algo(categories, _hashtables)

pandas/tests/arrays/categorical/test_constructors.py

@@ -42,7 +42,6 @@ def test_constructor_empty(self):
         expected = pd.Int64Index([1, 2, 3])
         tm.assert_index_equal(c.categories, expected)
 
-    @pytest.mark.xfail
     def test_constructor_empty_boolean(self):
         # see gh-22702
         cat = pd.CategoricalIndex([], categories=[True, False])