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
1251511305,PR_kwDOAMm_X844nz8j,6651,Typing support for custom backends,43316012,closed,0,,,4,2022-05-28T07:28:41Z,2022-06-04T10:17:55Z,2022-05-28T10:29:16Z,COLLABORATOR,,0,pydata/xarray/pulls/6651,"<!-- Feel free to remove check-list items aren't relevant to your change -->

- [x] Closes #6632

So far we have not found a good way of typing dynamically added custom backends (installed via pip).
So the only fallback option is to allow str.

I have decided to leave the Literal as type, since it gives the user a nice list of supported backends in the editor.
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6651/reactions"", ""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
1245726154,I_kwDOAMm_X85KQEXK,6632,Literal type of engine argument incompatible with custom backends,43316012,closed,0,,,5,2022-05-23T21:40:14Z,2022-05-28T10:29:16Z,2022-05-28T10:29:16Z,COLLABORATOR,,,,"### What is your issue?

In the recent typing improvements the `engine` argument for `open_dataset` was changed from Str to a Literal of xarrays internal engines.
This will cause problems for all third party backend plugins.

We have several possibilities:

1. I don't know if there is a way to know installed backends at type checking time. Then we could add this support. (I doubt this is possible seeing how dynamic these imports are)
2. Is it possible for these plugins to tell type checkers that their engine is valid, i.e. change the type signature of xarrays function? Then we should add a how-to in the docu.
3. Else we should probably revert to using Str.

Any typing experts here that could help?","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6632/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue