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regrid_dataset broken with xarray=0.16.1

See original GitHub issue

First off, thanks everyone for keeping this great package going!

Unfortunately, regridding of chunked/dask datasets seems to have broken with the latest 0.16.1 xarray release, maybe related to #4060?

Minimal Example

import xarray as xr
import xesmf as xe

ds = xr.tutorial.open_dataset('air_temperature').chunk({'time':1})
ds['foo'] = ds.air # adding a second field breaks regridder call
grid = xr.Dataset({'lat': (['lat'], ds.lat[::4]), 'lon': (['lon'], ds.lon[::4])})
regridder = xe.Regridder(ds, grid, 'bilinear')
ds_out = regridder(ds)

Fails with:

Traceback (most recent call last):
  File "test.py", line 8, in <module>
    ds_out = regridder(ds)
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xesmf/frontend.py", line 397, in __call__
    return self.regrid_dataset(indata, keep_attrs=keep_attrs)
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xesmf/frontend.py", line 515, in regrid_dataset
    ds_out = xr.apply_ufunc(
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xarray/core/computation.py", line 1092, in apply_ufunc
    return apply_dataset_vfunc(
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xarray/core/computation.py", line 410, in apply_dataset_vfunc
    result_vars = apply_dict_of_variables_vfunc(
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xarray/core/computation.py", line 356, in apply_dict_of_variables_vfunc
    result_vars[name] = func(*variable_args)
  File "/home/slevang/miniconda3/envs/salient/lib/python3.8/site-packages/xarray/core/computation.py", line 653, in apply_variable_ufunc
    raise ValueError(
ValueError: dimension 'dim1' in 'output_sizes' must correspond to output_core_dims

Regridding the tutorial dataset with single field air works fine, but adding a second variable raises this error with dimension names.