Backport PR #31207: BUG: no longer raise user warning when plotting tz aware time series (#31601)

Co-authored-by: Marco Gorelli <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v1.0.1.rst

@@ -103,7 +103,7 @@ I/O
 Plotting
 ^^^^^^^^
 
--
+- Plotting tz-aware timeseries no longer gives UserWarning (:issue:`31205`)
 -
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/timeseries.py

@@ -251,7 +251,7 @@ def _maybe_convert_index(ax, data):
         freq = frequencies.get_period_alias(freq)
 
         if isinstance(data.index, ABCDatetimeIndex):
-            data = data.to_period(freq=freq)
+            data = data.tz_localize(None).to_period(freq=freq)
         elif isinstance(data.index, ABCPeriodIndex):
             data.index = data.index.asfreq(freq=freq)
     return data

pandas/tests/plotting/test_datetimelike.py

@@ -45,11 +45,12 @@ def teardown_method(self, method):
 
     @pytest.mark.slow
     def test_ts_plot_with_tz(self, tz_aware_fixture):
-        # GH2877, GH17173
+        # GH2877, GH17173, GH31205
         tz = tz_aware_fixture
         index = date_range("1/1/2011", periods=2, freq="H", tz=tz)
         ts = Series([188.5, 328.25], index=index)
-        _check_plot_works(ts.plot)
+        with tm.assert_produces_warning(None):
+            _check_plot_works(ts.plot)
 
     def test_fontsize_set_correctly(self):
         # For issue #8765