AssertionError isinstance

[leguyader]

Describe the bug

With autoapi activated building the documentation fails. We don't really understand the error message or what's causing the issue and how to fix it.

How to Reproduce

$ git clone https://git.xfel.eu/SCS/ToolBox.git
$ cd ToolBox
$ git checkout autoapi-test
$ cd doc
$ make html

Expected behavior

The documentation should compile, but with autoapi it doesn't.

We get the following error:

Exception occurred:
  File "~/.local/lib/python3.8/site-packages/nbsphinx.py", line 1697, in apply
    assert isinstance(section.children[0], docutils.nodes.title)
AssertionError
The full traceback has been saved in /tmp/sphinx-err-qwdmz97v.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make: *** [Makefile:19: html] Error 2

Attached the corresponding traceback: log.txt

Your project

https://git.xfel.eu/SCS/ToolBox

Screenshots

No response

OS

unix

Python version

3.8.10

Sphinx version

4.2.0

Sphinx extensions

autoapi, nbsphinx

Extra tools

No response

Additional context

No response

[leguyader]

It looks like we are triggering some incompatibility between autoapi and nbsphinx. But I found this project https://forge.oasu.u-bordeaux.fr/jleconte/exo_k-public for example that uses both without problem. I confirmed it by building the documentation for this project locally.

I tried to copy some of the autoapi configuration from that exo_k project conf.py but nothing helped, we get an error from our documentation which we don't understand.

[AA-Turner]

Please provide a minimal reproducing example, ideally one page of documentation that triggers the bug.

Please also confirm it is not an issue with the extensions you mentioned but Sphinx itself.

A

[leguyader]

Looking for a minimal example, I found out that the error was triggered by 2 of our files having the following structure:

"""
    Class
    -----
"""

class Class:
    def __init__(self, num):
        self.num = num

The error is generated by line 3, '-----'