CFTimeIndex changes to normal Index after renaming

[ahuang11]

MCVE Code Sample

Since this code crashes for me and I don't have xarray master, I can't create a tested MCVE Code sample at the moment, but I think something along the lines of:

import xarray as xr
ds = xr.Dataset(coords={'time': xr.cftime_range(start='2000', periods=6, freq='2MS', calendar='noleap'), 'something': [0, 1, 2, 3]})
print(ds.indexes['time'])
ds = ds.rename({'something': 'something_else'})
print(ds.indexes['time'])

Expected Output

CFTimeIndex([2000-05-01 12:00:00, 2000-05-02 12:00:00,
             ...
             2001-04-01 12:00:00],
            dtype='object', name='time', length=425)

After renaming

Index([2000-05-01 12:00:00, 2000-05-02 12:00:00,
             ...
             2001-04-01 12:00:00],
            dtype='object', name='time', length=425)

Problem Description

CFTimeIndex changes to normal Index after renaming

Output of xr.show_versions()

Details

xarray: 0.14.0
pandas: 0.25.2
numpy: 1.17.2
scipy: 1.3.1
netCDF4: 1.5.3
pydap: None
h5netcdf: 0.7.4
h5py: 2.9.0
Nio: None
zarr: None
cftime: 1.0.4.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.0
cfgrib: None
iris: None
bottleneck: 1.2.1
dask: 2.6.0
distributed: 2.6.0
matplotlib: 3.1.1
cartopy: 0.17.0
seaborn: None
numbagg: None
setuptools: 41.4.0
pip: 19.3.1
conda: None
pytest: 5.2.1
IPython: 7.9.0
sphinx: None

[mathause]

The culprit may be in ds._rename_indexes:

xarray/xarray/core/dataset.py

Line 2662 in 40588dc

index = pd.Index(v, name=new_name)

where the index gets piped through pd.Index (even if it is not renamed):

import pandas as pd
pd.Index(ds.indexes['time'])

returns an Index instead of a CFTimeIndex

[keewis]

also, you can simplify that to

print(
    ds.indexes,
    ds.rename().indexes,
    ds.rename_dims().indexes,
    ds.rename_vars().indexes,
    sep="\n",
)

and the type of the index still gets dropped (on master)

[max-sixty]

Nice spot @mathause . We should be constructing from the type of v. pd.Index also has a method _shallow_copy IIRC we could call