Start emitting deprecation warning for Dataset.to_array (GH11721)

doc/whats-new.rst

@@ -143,6 +143,11 @@ Deprecations
   :py:attr:`DataTree.lineage` warns once instead of twice (:issue:`11721`,
   :pull:`11724`).
   By `Daisy DAI <https://github.com/ShinoKana>`_.
+- :py:meth:`Dataset.to_array` is deprecated in favor of :py:meth:`Dataset.to_dataarray`
+  but it did not emit any warning previously, now it emits a ``FutureWarning``
+  (:issue:`11721`, :pull:`11788`).
+  By `Soutrik Das <https://github.com/SoutrikDas>`_.
+
 
 
 Bug Fixes

xarray/core/dataset.py

@@ -7316,6 +7316,10 @@ def to_array(
         self, dim: Hashable = "variable", name: Hashable | None = None
     ) -> DataArray:
         """Convert this dataset into a DataArray (deprecated, use to_dataarray)."""
+        emit_user_level_warning(
+            "Dataset.to_array is deprecated, use Dataset.to_dataarray instead.",
+            FutureWarning,
+        )
         return self.to_dataarray(dim=dim, name=name)
 
     def _normalize_dim_order(

xarray/tests/test_dataset.py

@@ -3667,6 +3667,13 @@ def test_swap_dims(self) -> None:
         assert isinstance(actual.variables["x"], Variable)
         assert actual.xindexes["y"].equals(expected.xindexes["y"])
 
+    def test_to_array_deprecated(self) -> None:
+        ds = Dataset({"a": 1, "b": ("x", [1, 2, 3])}, coords={"c": 42})
+        expected = ds.to_dataarray("abc", name="foo")
+        with pytest.warns(FutureWarning, match=r"Dataset\.to_array is deprecated"):
+            actual = ds.to_array("abc", name="foo")
+        assert_identical(expected, actual)
+
     def test_expand_dims_error(self) -> None:
         original = Dataset(
             {