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
1228977960,PR_kwDOAMm_X843dwXx,6579,Fix Dataset/DataArray.isel with drop=True and scalar DataArray indexes,43316012,closed,0,,,1,2022-05-08T20:17:04Z,2022-05-11T17:19:53Z,2022-05-10T06:18:19Z,COLLABORATOR,,0,pydata/xarray/pulls/6579,"<!-- Feel free to remove check-list items aren't relevant to your change -->

- [x] Closes #6554
- [x] Tests added
- [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`

Additionally I have added new literal types for error handling (Only applied to functions related to isel such that mypy stops complaining).","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6579/reactions"", ""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
1222103599,I_kwDOAMm_X85I19Iv,6554,isel with drop=True does not drop coordinates if using scalar DataArray as indexer,43316012,closed,0,,,2,2022-05-01T10:14:37Z,2022-05-10T06:18:19Z,2022-05-10T06:18:19Z,COLLABORATOR,,,,"### What happened?

When using `DataArray/Dataset.isel` with `drop=True` with a scalar DataArray as indexer (see example) resulting scalar coordinates do not get dropped.
When using an integer the behavior is as expected.

### What did you expect to happen?

I expect that using a scalar DataArray behaves the same as an integer.

### Minimal Complete Verifiable Example

```Python
import xarray as xr

da = xr.DataArray([1, 2, 3], dims=""x"", coord={""k"": (""x"", [0, 1, 2])})
# <xarray.DataArray (x: 3)>
# array([1, 2, 3])
# Coordinates:
#     k        (x) int32 0 1 2

da.isel({""x"": 1}, drop=True)
# works
# <xarray.DataArray ()>
# array(2)

da.isel({""x"": xr.DataArray(1)}, drop=True)
# does not drop ""k"" coordinate
# <xarray.DataArray ()>
# array(2)
# Coordinates:
#     k        int32 1
```


### Relevant log output

_No response_

### Anything else we need to know?

_No response_

### Environment

<details>

INSTALLED VERSIONS
------------------
commit: 4fbca23a9fd8458ec8f917dd0e54656925503e90
python: 3.9.6 | packaged by conda-forge | (default, Jul  6 2021, 08:46:02) [MSC v.1916 64 bit (AMD64)]
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: AMD64 Family 23 Model 113 Stepping 0, AuthenticAMD
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('de_DE', 'cp1252')
libhdf5: 1.10.6
libnetcdf: 4.7.4

xarray: 0.18.2.dev76+g3a7e7ca2.d20210706
pandas: 1.3.0
numpy: 1.21.0
scipy: 1.7.0
netCDF4: 1.5.6
pydap: installed
h5netcdf: 0.11.0
h5py: 3.3.0
Nio: None
zarr: 2.8.3
cftime: 1.5.0
nc_time_axis: 1.3.1
PseudoNetCDF: installed
cfgrib: None
iris: 2.4.0
bottleneck: 1.3.2
dask: 2021.06.2
distributed: 2021.06.2
matplotlib: 3.4.2
cartopy: 0.19.0.post1
seaborn: 0.11.1
numbagg: 0.2.1
fsspec: 2021.06.1
cupy: None
pint: 0.17
sparse: 0.12.0
setuptools: 49.6.0.post20210108
pip: 21.3.1
conda: None
pytest: 6.2.4
IPython: None
sphinx: None

</details>
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6554/reactions"", ""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue