Add dt.date to plottable types (pydata#8873)

* Add dt.date to plottable types

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* Add new feature to whats-new.rst

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* Add test_date_dimension to plot tests

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* Add issue to whats-new

* Fix type in whats-new

* Fix 2 more typos in whats-new

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

doc/whats-new.rst

@@ -37,6 +37,8 @@ New Features
 - Allow creating :py:class:`xr.Coordinates` objects with no indexes (:pull:`8711`)
   By `Benoit Bovy <https://github.com/benbovy>`_ and `Tom Nicholas
   <https://github.com/TomNicholas>`_.
+- Enable plotting of ``datetime.dates``. (:issue:`8866`, :pull:`8873`)
+  By `Sascha Hofmann <https://github.com/saschahofmann>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/plot/utils.py

@@ -4,7 +4,7 @@
 import textwrap
 import warnings
 from collections.abc import Hashable, Iterable, Mapping, MutableMapping, Sequence
-from datetime import datetime
+from datetime import date, datetime
 from inspect import getfullargspec
 from typing import TYPE_CHECKING, Any, Callable, Literal, overload
 
@@ -672,7 +672,7 @@ def _ensure_plottable(*args) -> None:
         np.bool_,
         np.str_,
     )
-    other_types: tuple[type[object], ...] = (datetime,)
+    other_types: tuple[type[object], ...] = (datetime, date)
     cftime_datetime_types: tuple[type[object], ...] = (
         () if cftime is None else (cftime.datetime,)
     )

xarray/tests/test_plot.py

@@ -5,7 +5,7 @@
 import math
 from collections.abc import Hashable
 from copy import copy
-from datetime import datetime
+from datetime import date, datetime, timedelta
 from typing import Any, Callable, Literal
 
 import numpy as np
@@ -620,6 +620,18 @@ def test_datetime_dimension(self) -> None:
         ax = plt.gca()
         assert ax.has_data()
 
+    def test_date_dimension(self) -> None:
+        nrow = 3
+        ncol = 4
+        start = date(2000, 1, 1)
+        time = [start + timedelta(days=i) for i in range(nrow)]
+        a = DataArray(
+            easy_array((nrow, ncol)), coords=[("time", time), ("y", range(ncol))]
+        )
+        a.plot()
+        ax = plt.gca()
+        assert ax.has_data()
+
     @pytest.mark.slow
     @pytest.mark.filterwarnings("ignore:tight_layout cannot")
     def test_convenient_facetgrid(self) -> None: