fix sphinx version to 5.* since 6.0 is not supported by code

[vlad-khramov]

sphinx 6.0.0 was released several hours ago (https://github.com/sphinx-doc/sphinx/releases/tag/v6.0.0) and it is not supported by current code: example of filed docs build https://app.circleci.com/pipelines/github/ethereum/solidity/27991/workflows/8f12532e-1234-4041-80c3-e6d395958a30/jobs/1242177

I propose to fix version to 5.* as temporary fast solution

[github-actions]

Thank you for your contribution to the Solidity compiler! A team member will follow up shortly.

If you haven't read our contributing guidelines and our review checklist before, please do it now, this makes the reviewing process and accepting your contribution smoother.

If you have any questions or need our help, feel free to post them in the PR or talk to us directly on the #solidity-dev channel on Matrix.

[r0qs]

Hi @quantum13, thanks for your contribution.

Indeed, as we don't fix the versions of the dependencies, the recent update of sphinx to 6.0.0 dropped support to docutils 0.17 and as sphinx_rtd_theme does not have an official release with support to docutils 0.18 readthedocs/sphinx_rtd_theme#1302 (comment) the build of the documentation started to fail as you noted.

Maybe it is better to wait for the next sphinx_rtd_theme release?

[vlad-khramov]

@r0qs I do not insist. I just thought that better not to confuse contributors with broken docs build step (as I was confused in #13816).

Please close this PR if you think that better to wait.

[r0qs]

No problem at all, I totally agree with you. It is just because we recently had a similar situation with sphinx-a4doc in which the issue was quickly fixed upstream, and now I need to redo the workaround. So, it may be the case here as well.

As the documentation build is not critical, we can probably spend some time rethinking the current setup.
For instance, I would like to hear from others if we should change to a fixed version in the requeriments.txt instead of relying on minimum versions as it is now. Or if we should update the current minimum versions since they are already pretty outdated.

Any suggestion here @ekpyron @cameel ?

[nikola-matic]

@r0qs I would merge this and then either look for a more 'long term' solution later (e.g. pinning a specific version in requirements.txt as you suggested), or simply wait until it's fixed upstream (is there an issue in the sphinx repo for this?).
I'd like to just note, that docs is a required steps and is currently blocking merging anything.

[r0qs]

Ok. It is an issue in sphinx_rtd_theme and it was already fixed there, but not released yet. They have a release candidate version though.

[ekpyron]

We can give the release candidate a try.