id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
976207971,MDU6SXNzdWU5NzYyMDc5NzE=,5727,Setting item with loc and boolean mask fails,5802846,closed,0,,,3,2021-08-21T19:41:56Z,2022-03-17T17:11:43Z,2022-03-17T17:11:43Z,CONTRIBUTOR,,,,"**What happened**:
When setting a DataArray with `loc`, [xarray converts bool masks to the coord data type](https://github.com/pydata/xarray/blob/48a9dbe7d8dc2361bc985dd9fb1193a26135b310/xarray/core/indexing.py#L78). Therefore `loc` does not use a boolean mask but tries to match the indexes of the coord.

**Minimal Complete Verifiable Example**:

```python
import numpy as np
import xarray as xr


x = np.arange(10).astype(np.float64)
fx = np.arange(10).astype(np.float64)
da = xr.DataArray(fx,dims=['x'],coords={'x':x})
mask = np.zeros((10,))
mask[1::2] = 1
mask = mask.astype(bool)
da.loc[{'x':~mask}] = np.arange(5)+10
```


```
Traceback (most recent call last):
  File ""<stdin>"", line 1, in <module>
  File ""/home/matthmey/miniconda3/envs/analytics/lib/python3.7/site-packages/xarray/core/dataarray.py"", line 214, in __setitem__
    self.data_array[pos_indexers] = value
  File ""/home/matthmey/miniconda3/envs/analytics/lib/python3.7/site-packages/xarray/core/dataarray.py"", line 767, in __setitem__
    self.variable[key] = value
  File ""/home/matthmey/miniconda3/envs/analytics/lib/python3.7/site-packages/xarray/core/variable.py"", line 854, in __setitem__
    indexable[index_tuple] = value
  File ""/home/matthmey/miniconda3/envs/analytics/lib/python3.7/site-packages/xarray/core/indexing.py"", line 1164, in __setitem__
    array[key] = value
ValueError: shape mismatch: value array of shape (5,) could not be broadcast to indexing result of shape (10,)
```

**Anything else we need to know?**:
<del>Could be fixed by replacing [the line](https://github.com/pydata/xarray/blob/48a9dbe7d8dc2361bc985dd9fb1193a26135b310/xarray/core/indexing.py#L78), but maybe this is not the cleanest solution.</del> I tried fixing it with the following, which works for the above code but fails for other cases.
```
            if label.dtype != np.bool:
                label = maybe_cast_to_coords_dtype(label, coord.dtype)
```

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.0 (default, Oct  9 2018, 10:31:47) 
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 5.4.0-80-lowlatency
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: None
libnetcdf: None

xarray: 0.19.0
pandas: 1.0.1
numpy: 1.18.1
scipy: 1.4.1
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: 2.5.0
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2.14.0
distributed: None
matplotlib: 3.1.3
cartopy: None
seaborn: None
numbagg: None
pint: None
setuptools: 46.1.3.post20200330
pip: 20.0.2
conda: None
pytest: None
IPython: 7.13.0
sphinx: None



</details>
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