PEP 621: Remove invalid reference

[vstinner]

The reference is not rendered, not used, and it doesn't exist.

---

📚 Documentation preview 📚: https://pep-previews--3564.org.readthedocs.build/

[vstinner]

PEP 639 and PEP 739 point to https://packaging.python.org/en/latest/specifications/declaring-project-metadata/ ... which is now a HTTP 404 "Not Found" error.

[vstinner]

This change fix a build error on my PR #3560:

peps/pep-0621.rst:23: WARNING: undefined label: 'packaging:declaring-project-metadata'
...
make: *** [Makefile:22: html] Error 1

make dirhtml JOBS=$(nproc) runs PATH=.venv/bin:$PATH sphinx-build -b dirhtml -j 4 -W --keep-going -w sphinx-warnings.txt peps build where sphin-build -W option stands for: treat warnings as errors.

cc @brettcannon @hugovk

[hugovk]

We shouldn't delete canonical links to specs.

Please see #3563 which fixes it instead :)

[vstinner]

I'm not sure why Sphinx decided to emit a new warning. On the previous commit, the "Render PEPs" job didn't emit a warning: https://github.com/python/peps/actions/runs/7075200705/job/19257061142 sphinx-build was already run with -W option. And it was the same Sphinx version: Sphinx-7.2.6.

Before (success), versions:

Successfully installed Jinja2-3.1.2 MarkupSafe-2.1.3 Pygments-2.17.2 Sphinx-7.2.6 alabaster-0.7.13 babel-2.13.1 certifi-2023.11.17 charset-normalizer-3.3.2 colorama-0.4.6 coverage-7.3.2 docutils-0.20.1 idna-3.6 imagesize-1.4.1 iniconfig-2.0.0 livereload-2.6.3 packaging-23.2 pluggy-1.3.0 pytest-7.4.3 pytest-cov-4.1.0 requests-2.31.0 setuptools-69.0.2 six-1.16.0 snowballstemmer-2.2.0 sphinx-autobuild-2021.3.14 sphinxcontrib-applehelp-1.0.7 sphinxcontrib-devhelp-1.0.5 sphinxcontrib-htmlhelp-2.0.4 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-1.0.6 sphinxcontrib-serializinghtml-1.1.9 tornado-6.4 urllib3-2.1.0

On my PR, when the job failed, versions: same versions!

Successfully installed Jinja2-3.1.2 MarkupSafe-2.1.3 Pygments-2.17.2 Sphinx-7.2.6 alabaster-0.7.13 babel-2.13.1 certifi-2023.11.17 charset-normalizer-3.3.2 colorama-0.4.6 coverage-7.3.2 docutils-0.20.1 idna-3.6 imagesize-1.4.1 iniconfig-2.0.0 livereload-2.6.3 packaging-23.2 pluggy-1.3.0 pytest-7.4.3 pytest-cov-4.1.0 requests-2.31.0 setuptools-69.0.2 six-1.16.0 snowballstemmer-2.2.0 sphinx-autobuild-2021.3.14 sphinxcontrib-applehelp-1.0.7 sphinxcontrib-devhelp-1.0.5 sphinxcontrib-htmlhelp-2.0.4 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-1.0.6 sphinxcontrib-serializinghtml-1.1.9 tornado-6.4 urllib3-2.1.0

[hugovk]

Because we use intersphinx, which loads references from other Sphinx websites, in this case https://packaging.python.org.

Last night they merged a re-org which deleted a reference we were using.

[hugovk]

More on intersphinx: https://www.sphinx-doc.org/en/master/usage/extensions/intersphinx.html

We also use it to load references from CPython docs and the devguide, see these lines in the logs:

loading intersphinx inventory from https://docs.python.org/3/objects.inv...
loading intersphinx inventory from https://packaging.python.org/en/latest/objects.inv...
loading intersphinx inventory from https://devguide.python.org/objects.inv...
loading intersphinx inventory from https://docs.python.org/3.11/objects.inv...
loading intersphinx inventory from https://docs.python.org/3.12/objects.inv...

[vstinner]

Because we use intersphinx, which loads references from other Sphinx websites, in this case https://packaging.python.org/.

Oh, I didn't know this Sphinx feature.

[vstinner]

Follow-up: @hugovk wrote #3563