BUG: DataFrame.join on tz aware index and column

doc/source/whatsnew/v0.25.0.rst

@@ -297,6 +297,7 @@ Timezones
 - Bug in :func:`DataFrame.update` when updating with timezone aware data would return timezone naive data (:issue:`25807`)
 - Bug in :func:`to_datetime` where an uninformative ``RuntimeError`` was raised when passing a naive :class:`Timestamp` with datetime strings with mixed UTC offsets (:issue:`25978`)
 - Bug in :func:`to_datetime` with ``unit='ns'`` would drop timezone information from the parsed argument (:issue:`26168`)
+- Bug in :func:`DataFrame.join` where joining a timezone aware index with a timezone aware column would result in a column of ``NaN`` (:issue:`26335`)
 
 Numeric
 ^^^^^^^

pandas/core/reshape/merge.py

@@ -1674,8 +1674,8 @@ def _right_outer_join(x, y, max_groups):
 def _factorize_keys(lk, rk, sort=True):
     # Some pre-processing for non-ndarray lk / rk
     if is_datetime64tz_dtype(lk) and is_datetime64tz_dtype(rk):
-        lk = lk._data
-        rk = rk._data
+        lk = getattr(lk, '_values', lk)._data
+        rk = getattr(rk, '_values', rk)._data
 
     elif (is_categorical_dtype(lk) and
             is_categorical_dtype(rk) and

pandas/tests/reshape/merge/test_join.py

@@ -679,7 +679,7 @@ def test_join_multi_to_multi(self, join_type):
             right.join(left, on=['abc', 'xy'], how=join_type)
 
     def test_join_on_tz_aware_datetimeindex(self):
-        # GH 23931
+        # GH 23931, 26335
         df1 = pd.DataFrame(
             {
                 'date': pd.date_range(start='2018-01-01', periods=5,
@@ -697,7 +697,8 @@ def test_join_on_tz_aware_datetimeindex(self):
         )
         result = df1.join(df2.set_index('date'), on='date')
         expected = df1.copy()
-        expected['vals_2'] = pd.Series([np.nan] * len(expected), dtype=object)
+        expected['vals_2'] = pd.Series([np.nan] * 2 + list('tuv'),
+                                       dtype=object)
         assert_frame_equal(result, expected)