test_open_nczarr failing

[headtr1ck]

What is your issue?

In the latest CI runs it seems that test_backends.py::TestNCZarr::test_open_nczarr is failing with

KeyError: 'Zarr object is missing the attribute _ARRAY_DIMENSIONS and the NCZarr metadata, which are required for xarray to determine variable dimensions.'

I don't see an obvious reason for this, especially since the zarr version has not changed compared to some runs that were successful (2.13.6).

[malmans2]

The problem comes from libnetcdf. It bumped from 4.8.1 to 4.9.1.
I'll look into it.

[malmans2]

See: Unidata/netcdf-c#2647

The problem is that with netcdf-c=4.9.1 dimension names are lost when writing pure nczarr files. We only need it to make sure that xarray is able to read from pure nczarr.

[malmans2]

Slightly different issue related to the latest release of netcdf-c.

Looks like nczarr attribute key changed from "_NCZARR_ARRAY" to "_nczarr_array" (see Unidata/netcdf-c#2492), so we would have to take care of this if we want to keep supporting pure nczarr.

xarray/xarray/backends/zarr.py

Line 202 in 6531b57

os.path.basename(dim) for dim in zarray["_NCZARR_ARRAY"]["dimrefs"]