xarray.DataArray is not part of pint.Unit's upcast types?

[doronbehar]

So taking first steps with pint-xarray, I tried to do this:

import numpy as np
import pint_xarray
import xarray as xr
import pint
ureg = pint.UnitRegistry()

da = xr.DataArray(
    ureg.Quantity(
        np.array([2,3]),
        ureg.meter,
    ),
    coords={'person': ["a", "b"]},
)
ureg.kilogram/ da

And was surprised to find out it fails with:

Traceback (most recent call last):
  File "/home/doron/repos/lab-ion-trap-simulations/./t.py", line 17, in <module>
    ureg.kilogram / da
    ~~~~~~~~~~~~~~^~~~
  File "/nix/store/bb54xf04qx1j3hskjcyjwzhbnkhi666m-python3-3.12.8-env/lib/python3.12/site-packages/pint/facets/plain/unit.py", line 167, in __truediv__
    return self._REGISTRY.Quantity(1 / other, self._units)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/bb54xf04qx1j3hskjcyjwzhbnkhi666m-python3-3.12.8-env/lib/python3.12/site-packages/pint/facets/plain/quantity.py", line 190, in __new__
    raise TypeError(f"PlainQuantity cannot wrap upcast type {type(value)}")
TypeError: PlainQuantity cannot wrap upcast type <class 'xarray.core.dataarray.DataArray'>

Whereas:

da**-1 * ureg.kilogram
ureg.kilogram * 1/da
1*ureg.kilogram / da
ureg.kilogram * da # Different meaning of course

Don't fail. This issue was originally posted at xarray-contrib/pint-xarray#289 but I got convinced that the fix for it should be done here and not there, as pint explicitly puts xarray.DataArray (and probably xarray.Dataset as well) in the "upcast types" list.