broken output of `find_root_and_group` for h5netcdf

[kmuehlbauer]

MCVE Code Sample

# Your code here
import netCDF4
import h5netcdf
import xarray
from xarray.backends.common import find_root_and_group
root = netCDF4.Dataset("test.nc", "w", format="NETCDF4")
test1 = root.createGroup("test1")
test1.createGroup("test2")
root.close()
h5n = h5netcdf.File('test.nc')
print(find_root_and_group(h5n['test1'])[1])
h5n.close()

This will output:
//test1//test1/test2

Expected Output

/test1/test2

Problem Description

I stumbled over this while working on #3618. Although the function claims to retrieve root and group name of netCDF4/h5netcdf datasets the output for h5netcdf is broken.

Output of xr.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.8.0 | packaged by conda-forge | (default, Nov 22 2019, 05:03:59)
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 4.12.14-lp151.28.36-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: de_DE.UTF-8
LOCALE: de_DE.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.7.3

xarray: 0.14.1+43.g3e9d9046.dirty
pandas: 0.25.3
numpy: 1.17.3
scipy: 1.3.3
netCDF4: 1.5.3
pydap: None
h5netcdf: 0.7.4
h5py: 2.10.0
Nio: None
zarr: None
cftime: 1.0.4.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2.8.0
distributed: 2.9.0
matplotlib: 3.1.2
cartopy: 0.17.0
seaborn: None
numbagg: None
setuptools: 42.0.2.post20191201
pip: 19.3.1
conda: None
pytest: 5.3.1
IPython: 7.10.2
sphinx: 2.3.1

[kmuehlbauer]

Good chance that this might be an h5netcdf issue. Can someone double check?

[kmuehlbauer]

After a bit of further investigation, looks like this is indeed a problem with how h5netcdf retrieves the .name. While netCDF4 gives back just the name of a group h5netcdf gives back the hdf5 name which is the full path to the group.

# Your code here
import netCDF4
import h5netcdf
import xarray
from xarray.backends.common import find_root_and_group
root = netCDF4.Dataset("testx.nc", "w", format="NETCDF4")
test1 = root.createGroup("test1")
test1.createGroup("test2")
print(root['test1/test2'].name)
root.close()
h5n = h5netcdf.File('testx.nc')
print(h5n['test1/test2'].name)
h5n.close()

Output:

test2
/test1/test2

[kmuehlbauer]

temporarily fixed by #3618 . This is now tracked in h5netcdf/h5netcdf#68.

[kmuehlbauer]

A bit more of context:

As it turns out, the temporary fix will be permanent for the time being. This is because h5netcdf aligns with h5py(returning full path) for it's new API. The legacyapi (netCDF4 drop-in) will return single group name (not full path).