CanonicalPyPASpecBanner or Intersphinx fails on RTD?

[ambv]

Currently the RTD build is failing. For example: https://readthedocs.org/projects/pep-previews/builds/22823671/

It's weird, it doesn't reproduce for me locally. It's:

[2Kwriting output... [ 11%] pep-0000 .. pep-0257
/home/docs/checkouts/readthedocs.org/user_builds/pep-previews/checkouts/3562/peps/pep-0621.rst:23: WARNING: undefined label: 'packaging:declaring-project-metadata'

This is an Intersphinx reference handled by CanonicalPyPASpecBanner, and locally for me it works just fine. It renders as the pop-up banner with the correct link to https://packaging.python.org/en/latest/specifications/pyproject-toml/#pyproject-toml-spec.

Yet on RTD this doesn't work.

@CAM-Gerlach, any ideas?

[hugovk]

The build failure is caused by pypa/packaging.python.org#1434 and already fixed in main: #3563.

We'll need to merge main into old PRs to fix them, unless the packaging guide merges the PR above. I'll leave a note there.