Missing dependency ecmwf-opendata causes plugin loading to fail

[francesconazzaro]

When importing xarray and listing available engines, I get a warning related to the ECMWF plugin failing to load due to a missing module: ecmwf.opendata.

Steps to reproduce

$ uv run python
Python 3.12.11 (main, Jul 22 2025, 01:45:44) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import xarray
>>> engines = xarray.backends.plugins.list_engines()
/venv/lib/python3.12/site-packages/xarray/backends/plugins.py:110: RuntimeWarning: Engine 'ecmwf' loading failed:
No module named 'ecmwf.opendata'
  external_backend_entrypoints = backends_dict_from_pkg(entrypoints_unique)
>>> print(engines.keys())
dict_keys(['scipy', 'cfgrib', 'rasterio', 'sentinel-1', 'store', 'zarr'])

As you can see, after the warning, the ecmwf engine is not listed among the available backends.

If ecmwf-opendata is required for the ECMWF backend to work, it should probably be listed under the dependencies section in pyproject.toml.

[francesconazzaro]

Closed by #6