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
1695809136,I_kwDOAMm_X85lE_5w,7816,"Backend registration does not match docs, and is no longer specifiable in maturin pyproject toml",56827,closed,0,,,7,2023-05-04T11:17:08Z,2023-05-05T08:55:57Z,2023-05-05T08:46:42Z,NONE,,,,"### What happened?

https://docs.xarray.dev/en/stable/internals/how-to-add-new-backend.html#how-to-register-a-backend does not work with maturin any more. The format has changed to a tuple, from netcdf4 backend:

BACKEND_ENTRYPOINTS[""netcdf4""] = (""netCDF4"", NetCDF4BackendEntrypoint)

https://www.maturin.rs/metadata.html

is this specifiable by pyproject.toml anymore?

Affects: #7446 

### What did you expect to happen?

_No response_

### Minimal Complete Verifiable Example

_No response_

### 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](https://mybinder.org/v2/gh/pydata/xarray/main?urlpath=lab/tree/doc/examples/blank_template.ipynb), 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

<details>



</details>
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