Skip one more hypothesis test for dtype string (#11152)

Includes a few small fixes:

* When the key is `dim` using **kwargs doesn't yield the same result as
using the positional argument. Consider making this a positional
argument only field in the future.

* Coerce pd.Index to object if string dtype fails

Author: jsignell

properties/test_index_manipulation.py

@@ -269,6 +269,13 @@ def assert_invariants(self):
 DatasetTest = DatasetStateMachine.TestCase
 
 
+@pytest.mark.skip(reason="failure detected by hypothesis")
+def test_unstack_string():
+    ds = xr.Dataset()
+    ds["0"] = np.array(["", "0", "\x000"], dtype="<U2")
+    ds.stack({"1": ["0"]}).unstack()
+
+
 @pytest.mark.skip(reason="failure detected by hypothesis")
 def test_unstack_object():
     ds = xr.Dataset()

xarray/core/dataset.py

@@ -5205,7 +5205,7 @@ def _stack_once(
                 vdims = list(var.dims) + add_dims
                 shape = [self.sizes[d] for d in vdims]
                 exp_var = var.set_dims(vdims, shape)
-                stacked_var = exp_var.stack(**{new_dim: dims})
+                stacked_var = exp_var.stack({new_dim: dims})
                 new_variables[name] = stacked_var
                 stacked_var_names.append(name)
             else:

xarray/core/indexes.py

@@ -536,7 +536,13 @@ def safe_cast_to_index(array: Any) -> pd.Index:
                 )
                 kwargs["dtype"] = "float64"
 
-        index = pd.Index(to_numpy(array), **kwargs)
+        values = to_numpy(array)
+        try:
+            index = pd.Index(values, **kwargs)
+        except UnicodeEncodeError:
+            # coerce to object if pandas fails to coerce to string
+            kwargs["dtype"] = "object"
+            index = pd.Index(values, **kwargs)
 
     return _maybe_cast_to_cftimeindex(index)