auto_complex appears to be broken for DataTrees

[EmDash00]

What happened?

Running the example code in the documentation with a DataTree appears to be broken. The data is read back in encoded form rather than turned automatically into a complex number.

What did you expect to happen?

The datatree's datasets should respect auto_complex and read back the encoded data as complex numbers.

Minimal Complete Verifiable Example

import xarray as xr
import numpy as np

data = np.array([[1 + 2j, 3 + 4j], [5 + 6j, 7 + 8j]])
dt2 = xr.DataTree(
    xr.Dataset({'data': xr.DataArray(
        data,
        dims=["x", "y"],
        coords={"x": ["a", "b"], "y": [1, 2]},
        name="complex_nums",
    )})
)

# write the data to disk
dt2.to_netcdf("complex_nums_nc4.nc", engine="netcdf4", auto_complex=True)
# read the file back into memory
with xr.open_datatree(
    "complex_nums_nc4.nc", engine="netcdf4", auto_complex=True
) as dt_nc4:

    print(dt_nc4['data'].dtype)
   # prints: {'names': ['r', 'i'], 'formats': ['<f8', '<f8'], 'offsets': [0, 8], 'itemsize': 16, 'aligned': True}

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

Anything else we need to know?

No response

Environment

[kmuehlbauer]

Thanks @EmDash00 for filing that issue. I can reproduce, root cause is auto_complex-kwarg isn't distributed down to NetCDF4DataStore.open for open_datatree.

[kmuehlbauer]

@EmDash00 fix in #10632.