deprecate the cdms2 conversion methods (pydata#7876)

* emit deprecation warnings for the cdms2 conversion methods

* add the deprecation notice to the docstring

* check that the deprecation warnings are properly raised

* actually check that the deprecation message mentions cdms2

* skip cdms2 checks for new numpy / python versions

* whats-new entry

* make the deprecation message consistent

* functions → methods

* adjust the skip condition

* maintenance mode → deprecated

doc/whats-new.rst

@@ -30,6 +30,8 @@ Breaking changes
 
 Deprecations
 ~~~~~~~~~~~~
+- Deprecate the `cdms2 <https://github.com/CDAT/cdms>`_ conversion methods (:pull:`7876`)
+  By `Justus Magin <https://github.com/keewis>`_.
 
 Performance
 ~~~~~~~~~~~

xarray/core/dataarray.py

@@ -42,6 +42,7 @@
     ReprObject,
     _default,
     either_dict_or_kwargs,
+    emit_user_level_warning,
 )
 from xarray.core.variable import (
     IndexVariable,
@@ -4331,16 +4332,44 @@ def from_series(cls, series: pd.Series, sparse: bool = False) -> DataArray:
         return result
 
     def to_cdms2(self) -> cdms2_Variable:
-        """Convert this array into a cdms2.Variable"""
+        """Convert this array into a cdms2.Variable
+
+        .. deprecated:: 2023.06.0
+            The `cdms2`_ library has been deprecated. Please consider using the
+            `xcdat`_ library instead.
+
+        .. _cdms2: https://github.com/CDAT/cdms
+        .. _xcdat: https://github.com/xCDAT/xcdat
+        """
         from xarray.convert import to_cdms2
 
+        emit_user_level_warning(
+            "The cdms2 library has been deprecated."
+            " Please consider using the xcdat library instead.",
+            DeprecationWarning,
+        )
+
         return to_cdms2(self)
 
     @classmethod
     def from_cdms2(cls, variable: cdms2_Variable) -> DataArray:
-        """Convert a cdms2.Variable into an xarray.DataArray"""
+        """Convert a cdms2.Variable into an xarray.DataArray
+
+        .. deprecated:: 2023.06.0
+            The `cdms2`_ library has been deprecated. Please consider using the
+            `xcdat`_ library instead.
+
+        .. _cdms2: https://github.com/CDAT/cdms
+        .. _xcdat: https://github.com/xCDAT/xcdat
+        """
         from xarray.convert import from_cdms2
 
+        emit_user_level_warning(
+            "The cdms2 library has been deprecated."
+            " Please consider using the xcdat library instead.",
+            DeprecationWarning,
+        )
+
         return from_cdms2(variable)
 
     def to_iris(self) -> iris_Cube:

xarray/tests/test_dataarray.py

@@ -3548,6 +3548,10 @@ def test_to_masked_array(self) -> None:
         ma = da.to_masked_array()
         assert len(ma.mask) == N
 
+    @pytest.mark.skipif(
+        Version(np.__version__) > Version("1.24") or sys.version_info[:2] > (3, 10),
+        reason="cdms2 is unmaintained and does not support newer `numpy` or python versions",
+    )
     def test_to_and_from_cdms2_classic(self) -> None:
         """Classic with 1D axes"""
         pytest.importorskip("cdms2")
@@ -3565,7 +3569,8 @@ def test_to_and_from_cdms2_classic(self) -> None:
             IndexVariable("distance", [-2, 2]),
             IndexVariable("time", [0, 1, 2]),
         ]
-        actual = original.to_cdms2()
+        with pytest.deprecated_call(match=".*cdms2"):
+            actual = original.to_cdms2()
         assert_array_equal(actual.asma(), original)
         assert actual.id == original.name
         assert tuple(actual.getAxisIds()) == original.dims
@@ -3578,7 +3583,8 @@ def test_to_and_from_cdms2_classic(self) -> None:
         assert len(component_times) == 3
         assert str(component_times[0]) == "2000-1-1 0:0:0.0"
 
-        roundtripped = DataArray.from_cdms2(actual)
+        with pytest.deprecated_call(match=".*cdms2"):
+            roundtripped = DataArray.from_cdms2(actual)
         assert_identical(original, roundtripped)
 
         back = from_cdms2(actual)
@@ -3587,6 +3593,10 @@ def test_to_and_from_cdms2_classic(self) -> None:
         for coord_name in original.coords.keys():
             assert_array_equal(original.coords[coord_name], back.coords[coord_name])
 
+    @pytest.mark.skipif(
+        Version(np.__version__) > Version("1.24") or sys.version_info[:2] > (3, 10),
+        reason="cdms2 is unmaintained and does not support newer `numpy` or python versions",
+    )
     def test_to_and_from_cdms2_sgrid(self) -> None:
         """Curvilinear (structured) grid
 
@@ -3605,7 +3615,8 @@ def test_to_and_from_cdms2_sgrid(self) -> None:
             coords=dict(x=x, y=y, lon=lon, lat=lat),
             name="sst",
         )
-        actual = original.to_cdms2()
+        with pytest.deprecated_call():
+            actual = original.to_cdms2()
         assert tuple(actual.getAxisIds()) == original.dims
         assert_array_equal(original.coords["lon"], actual.getLongitude().asma())
         assert_array_equal(original.coords["lat"], actual.getLatitude().asma())
@@ -3616,6 +3627,10 @@ def test_to_and_from_cdms2_sgrid(self) -> None:
         assert_array_equal(original.coords["lat"], back.coords["lat"])
         assert_array_equal(original.coords["lon"], back.coords["lon"])
 
+    @pytest.mark.skipif(
+        Version(np.__version__) > Version("1.24") or sys.version_info[:2] > (3, 10),
+        reason="cdms2 is unmaintained and does not support newer `numpy` or python versions",
+    )
     def test_to_and_from_cdms2_ugrid(self) -> None:
         """Unstructured grid"""
         pytest.importorskip("cdms2")
@@ -3626,7 +3641,8 @@ def test_to_and_from_cdms2_ugrid(self) -> None:
         original = DataArray(
             np.arange(5), dims=["cell"], coords={"lon": lon, "lat": lat, "cell": cell}
         )
-        actual = original.to_cdms2()
+        with pytest.deprecated_call(match=".*cdms2"):
+            actual = original.to_cdms2()
         assert tuple(actual.getAxisIds()) == original.dims
         assert_array_equal(original.coords["lon"], actual.getLongitude().getValue())
         assert_array_equal(original.coords["lat"], actual.getLatitude().getValue())