renaming index variables with rename_vars seems buggy

[dcherian]

What happened?

(xref #8658)

I'm not sure what the expected behaviour is here:

import xarray as xr
import numpy as np
from xarray.testing import _assert_internal_invariants

ds = xr.Dataset()
ds.coords["1"] = ("1", np.array([1], dtype=np.uint32))
ds["1_"] = ("1", np.array([1], dtype=np.uint32))
ds = ds.rename_vars({"1": "0"})
ds

It looks like this sequence of operations creates a default index

But then

from xarray.testing import _assert_internal_invariants

_assert_internal_invariants(ds, check_default_indexes=True)

fails with

...
File ~/repos/xarray/xarray/testing/assertions.py:301, in _assert_indexes_invariants_checks(indexes, possible_coord_variables, dims, check_default)
    299 if check_default:
    300     defaults = default_indexes(possible_coord_variables, dims)
--> 301     assert indexes.keys() == defaults.keys(), (set(indexes), set(defaults))
    302     assert all(v.equals(defaults[k]) for k, v in indexes.items()), (
    303         indexes,
    304         defaults,
    305     )

AssertionError: ({'0'}, set())

[benbovy]

That looks right to me.

• ds.coords["1"] = ("1", np.array([1], dtype=np.uint32)) creates an index by default (setting a dimension coordinate)
• since the index refactor ds = ds.rename_vars({"1": "0"}) preserves the coordinate index
• _assert_internal_invariants(ds, check_default_indexes=True) fails as expected (presence of a non-dimension index after renaming the coordinate "1" -> "0".