export to requirements.in

[aucampia]

Actual problem

I have this pyproject.toml and poetry.lock.

The resulting version for Sphinx is 4, however, if only the main dependency group and docs dependency group is considered then the version can be 5.x, even maybe 6, I think.

I would really like to build on readthedocs with Sphinx 5 at least, and I can kind of do it but I think it would be much simpler if I could rather just export the constraints inside pyproject.toml to requirements.in and then use pip-compile, or just pip install -r ... it.

This came up while working on RDFLib/rdflib#2187

Suggestion

Add support for --format=requirements.in in poetry-plugin-export. What this would do is basically take the selected extras and groups from pyproject.toml and copy them verbatim to requirements.in. It would not consider the poetry.lock file at all.