issues: 544371612

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
544371612 MDU6SXNzdWU1NDQzNzE2MTI= 3657 .rename() does not check conflict with multiindex level names 14136435 closed 0     0 2020-01-01T15:50:38Z 2020-01-03T12:16:45Z 2020-01-03T12:16:45Z CONTRIBUTOR      

MCVE Code Sample

```python

import xarray as xr ds = xr.Dataset({"x": 42}, {"level0": [0, 1], "level1": [3, 4]}).set_index(mindex=["level0", "level1"]) ds <xarray.Dataset> Dimensions: (mindex: 2) Coordinates: * mindex (mindex) MultiIndex - level0 (mindex) int64 0 1 - level1 (mindex) int64 3 4 Data variables: x int64 42 ds.rename({"x": "level0"}) <xarray.Dataset> Dimensions: (mindex: 2) Coordinates: * mindex (mindex) MultiIndex - level0 (mindex) int64 0 1 - level1 (mindex) int64 3 4 Data variables: level0 int64 42 ```

Expected Output

raise a ValueError("conflicting Multiindex names ...")

Problem Description

Using .rename() you can get into a situation where you have a data variable or coordinate with the same name as a multi-index level name.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: b3d3b4480b7fb63402eb6c02103bb8d6c7dbf93a python: 3.8.0 | packaged by conda-forge | (default, Nov 22 2019, 19:11:38) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.4.0-18362-Microsoft machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: None libnetcdf: None xarray: 0.14.1+36.gb3d3b44 pandas: 0.25.3 numpy: 1.18.0 scipy: None netCDF4: None pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: None nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.9.1 distributed: 2.9.1 matplotlib: None cartopy: None seaborn: None numbagg: None setuptools: 42.0.2.post20191201 pip: 19.3.1 conda: None pytest: 5.3.2 IPython: None sphinx: None 
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   completed 13221727 issue

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