xarray.DataArray.weighted performs unweighted mean if dimension names differ without any warning

What happened?

dataarray.weighted(weights).mean() performs an unweighted mean if dimensions of weights and to-be-weighted-array differ. That is ok, but a warning message informing of it would be very helpful, as currently the mean is just performed and the user may assume that a weighted mean happenned.

What did you expect to happen?

I would expect to get a warning when performing the mean, knowing that it is not using the weights that it got assigned.

Minimal Complete Verifiable Example

import xarray as xr
import numpy as np
test_array = xr.DataArray(np.array([0,1,2]),
                     dims=('dim1'),
            )
weights = xr.DataArray(np.array([1,50,100]),
                     dims=('dim1'),
            )
weights2 = xr.DataArray(np.array([1,50,100]),
                     dims=('dim2'),
            )
# apply weights
test_array_weighted = test_array.weighted(weights)
#now apply weights with different dimension name
test_array_weighted2 = test_array.weighted(weights2)
# compute weighted mean
if (test_array_weighted.mean() != test_array_weighted2.mean()):
    print ('Different means')
    print ('test_array_weighted.mean=',test_array_weighted.mean())
    print ('test_array_weighted2.mean=',test_array_weighted2.mean())

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.

Relevant log output

No response

Anything else we need to know?

No response

Environment

Start by reproducing the Minimal Complete Verifiable Example with xarray.DataArray.weighted(), comparing weights with matching and differing dimension names. Trace the weighted mean behavior and add coverage for the differing-dimension case; done means the unweighted fallback emits a warning while the matching-dimension case remains unchanged.