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
624424922,MDU6SXNzdWU2MjQ0MjQ5MjI=,4093,rename_dims to an existing dimension name,2448579,closed,0,,,2,2020-05-25T18:00:28Z,2020-05-25T19:35:09Z,2020-05-25T19:35:08Z,MEMBER,,,,"```
ds = xr.Dataset({""a"": (""x"", np.arange(10)), ""b"": (""y"", np.arange(10))})
ds.rename_dims({""x"": ""y""})
```
```
ValueError: Cannot rename x to y because y already exists. Try using swap_dims instead.
```

This should be possible since both `x` and `y` have the same lengths. 
Thoughts?

For indexed dimensions, should we check that the indexes are equal?
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/4093/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue