ValueError: too many values to unpack

[sedimentation-fault]

Description
While building the references of Sage 9.0, I got:

# Sphinx version: 2.0.1
# Python version: 3.7.6 (CPython)
# Docutils version: 0.15.2 release
# Jinja2 version: 2.11.1
# Last messages:

# Loaded extensions:
Traceback (most recent call last):
  File "/usr/lib/python3.7/site-packages/sphinx/cmd/build.py", line 283, in build_main
    args.tags, args.verbosity, args.jobs, args.keep_going)
  File "/usr/lib/python3.7/site-packages/sphinx/application.py", line 260, in __init__
    self._init_builder()
  File "/usr/lib/python3.7/site-packages/sphinx/application.py", line 321, in _init_builder
    self.emit('builder-inited')
  File "/usr/lib/python3.7/site-packages/sphinx/application.py", line 440, in emit
    return self.events.emit(event, self, *args)
  File "/usr/lib/python3.7/site-packages/sphinx/events.py", line 76, in emit
    results.append(callback(*args))
  File "/usr/lib/python3.7/site-packages/sphinx/ext/intersphinx.py", line 207, in load_mappings
    for key, (name, (uri, invs)) in app.config.intersphinx_mapping.items():
ValueError: too many values to unpack (expected 2)

How To Reproduce
Steps to reproduce the behavior:
I have written a detailed account in:
cschwan/sage-on-gentoo#580

Expected behavior
No error should occur.

Your project
Sage 9.0 on Gentoo. Using the sage-9.0-r1 ebuild from the sage-on-gentoo overlay: https://github.com/cschwan/sage-on-gentoo

Environment info
See error text above.

Reason
The error occurs in

/usr/lib/python3.7/site-packages/sphinx/ext/intersphinx.py", line 207

According to #3075, it is due to a change that took place in sphinx 1.4:

This is incompatible change since 1.4 (see #2320).
After the change, the entries was changed to a list of entryname, (links, subitems, key).

Could it be that this change didn't reach line 207 of intersphinx.py yet?

[tk0miya]

Please let me know your intersphinx_mapping settings. What value did you set?

[sedimentation-fault]

Oops...good question - I must confess, I have no idea! Now I feel like a newbie! 🐤 :-)

Let's see: I am trying to compile sage-9.0 and I am stuck at its documentation, which, with sphinx-2.0.1 (and only that! all other versions, from 1.7.5 to 1.8.5 and 2.4.4 break earlier with other errors) breaks at the second pass of the references - you can see the error at the link I posted.

About the intersphinx_mapping...using ripgrep I found it at

sage-9.0/src/sage/docs/conf.py

# Cross-links to other project's online documentation.
python_version = sys.version_info.major
intersphinx_mapping = {
    'python': ('https://docs.python.org/',
                os.path.join(SAGE_DOC_SRC, "common",
                             "python{}.inv".format(python_version))),
    'pplpy': (PPLPY_DOCS, None)}

def set_intersphinx_mappings(app):
    """
    Add precompiled inventory (the objects.inv)
    """
    refpath = os.path.join(SAGE_DOC, "html", "en", "reference")
    invpath = os.path.join(SAGE_DOC, "inventory", "en", "reference")
    if app.config.multidoc_first_pass == 1 or \
            not (os.path.exists(refpath) and os.path.exists(invpath)):
        app.config.intersphinx_mapping = {}
        return

    app.config.intersphinx_mapping = intersphinx_mapping

    # Add master intersphinx mapping
    dst = os.path.join(invpath, 'objects.inv')
    app.config.intersphinx_mapping['sagemath'] = (refpath, dst)

Now, before you continue please have a look at

https://trac.sagemath.org/ticket/28856

where some important details might be lurking. For example, it is said there that "our intersphinx usage differs from normal usage" - but I have no idea in which respect...

[tk0miya]

Thank you for the info. It seems sagemath docs try to configure via Sphinx events. And it does not work since 2.x because we've refactored the intersphinx. Sorry for inconvenience. But I don't know such hack...
Please let them know to use config-inited event instead of builder-inited event. And I'll work to allow customizing intersphinx_mapping on the event on 3.0.

[tk0miya]

I just merged #7415. It allows extensions to modify configurations via config-inited event. In this case, sagemath should be fixed to use the event and new Sphinx.

[sedimentation-fault]

Thank you very much! I will forward this information to the sage-on-gentoo project.

[timokau]

Thanks a lot for going the extra mile and fixing our hacks for us. That is far beyond any responsibility I would have assigned to an upstream project :)

As I said in the trac ticket, I don't really know why we aren't using intersphinx as its supposed to be used. But at least now we'll be able to fix our build with an up-to-date sphinx.