BUG: Sphinx Crashes When `doctest-remote-data-all` Is At Top Of File

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Introduction

Sphinx is a popular tool for generating documentation from reStructuredText (RST) files. However, it can sometimes crash when encountering certain directives or configurations. In this article, we will explore a specific issue where Sphinx crashes when the doctest-remote-data-all directive is placed at the top of an RST file.

Background

The doctest-remote-data-all directive is used to enable remote data for doctests. It can be placed anywhere in the RST file, and it will skip the remaining parts unless remote data is enabled. However, when placed at the top of the file, Sphinx crashes with an IndexError.

Versions

The following versions of Sphinx and its dependencies were used to reproduce the issue:

  • Sphinx version: 8.2.3
  • Python version: 3.13.3 (CPython)
  • Docutils version: 0.21.2
  • Jinja2 version: 3.1.6
  • Pygments version: 2.19.1

Error Message

The full error message is as follows:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/cmd/build.py", line 432, in build_main
    app.build(args.force_all, args.filenames)
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/application.py", line 426, in build
    self.builder.build_update()
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/builders/__init__.py", line 375, in build_update
    self.build(
    ~~~~~~~~~~^
        to_build,
        ^^^^^^^^^
    ...<2 lines>...
        method='update',
        ^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/builders/__init__.py", line 403, in build
    updated_docnames = set(self.read())
                               ~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/builders/__init__.py", line 519, in read
    self._read_serial(docnames)
        ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/builders/__init__.py", line 584, in _read_serial
    self.read_doc(docname)
        ~~~~~~~~~~~~~^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/builders/__init__.py", line 648 in read_doc
    publisher.publish()
        ~~~~~~~~~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/core.py", line 234, in publish
    self.document = self.reader.read(self.source, self.parser,
                        ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
                                         self.settings)
                                         ^^^^^^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/io.py", line 103, in read
    self.parse()
        ~~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/readers/__init__.py", line 76, in parse
    self.parser.parse(self.input, document)
        ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/sphinx/parsers.py", line 86, in parse
    self.statemachine.run(inputlines, document, inliner=self.inliner)
        ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/parsers/rst/states.py", line 169, in run
    results = StateMachineWS.run(self, input_lines, input_offset,
                                     input_source=document['source'])
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/statemachine.py", line 233, in run
        context, next_state, result = self.check_line(
                                      ~~~~~~~~~~~~~~~^
            context, state, transitions)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/statemachine.py", line 445, in check_line
        return method(match, context, next_state)
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/parsers/rst/states.py", line 2357, in explicit_markup
        nodelist, blank_finish = self.explicit_construct(match)
                                 ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/parsers/rst/states.py", line 2369, in explicit_construct
        return method(self, expmatch)
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/parsers/rst/states.py", line 2106, in directive
        return self.run_directive(
               ~~~~~~~~~~~~~~~~~~^
            directive_class, match, type_name, option_presets)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/docs/checkouts/readocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/parsers/rst/states.py", line 2156, in run_directive
        result = directive_instance.run()
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/pytest_doctestplus/sphinx/doctestplus.py", line 23, in run
        if re.match('win32', self.content[0]):
                             ~~~~~~~~~~~~^^^
      File "/home/docs/checkouts/readthedocs.org/user_builds/astropy/conda/17839/lib/python3.13/site-packages/docutils/statemachine.py", line 1136, in __getitem__
        return self.data[i]
               ~~~~~~~~~^^^
    IndexError: list index out of range

Analysis

The error message indicates that an IndexError occurs when trying to access the first element of the content list in the doctestplus directive. This suggests that the content list is empty, which is likely due to the fact that the doctest-remote-data-all directive is placed at the top of the file.

Workaround

To avoid this issue, it is recommended to place the doctest-remote-data-all directive anywhere in the RST file, except at the top. This will ensure that the directive is processed correctly and does not cause Sphinx to crash.

Conclusion

In conclusion, the doctest-remote-data-all directive can cause Sphinx to crash when placed at the top of an RST file. To avoid this issue, it is recommended to place the directive anywhere in the file, except at the top. This will ensure that Sphinx processes the directive correctly and generates the documentation without errors.

Additional Information

For more information on this issue, please refer to the following GitHub pull request and Read the Docs build:

Q: What is the doctest-remote-data-all directive?

A: The doctest-remote-data-all directive is used to enable remote data for doctests. It allows doctests to access remote data sources, such as online databases or APIs.

Q: Why does Sphinx crash when doctest-remote-data-all is at the top of the file?

A: Sphinx crashes when doctest-remote-data-all is at the top of the file because it causes an IndexError when trying to access the first element of the content list in the doctestplus directive. This is likely due to the fact that the content list is empty when the directive is placed at the top of the file.

Q: How can I avoid this issue?

A: To avoid this issue, you can place the doctest-remote-data-all directive anywhere in the RST file, except at the top. This will ensure that the directive is processed correctly and does not cause Sphinx to crash.

Q: What are the consequences of placing doctest-remote-data-all at the top of the file?

A: Placing doctest-remote-data-all at the top of the file will cause Sphinx to crash with an IndexError. This will prevent the documentation from being generated correctly and may result in errors or warnings being displayed.

Q: Can I use doctest-remote-data-all with other directives?

A: Yes, you can use doctest-remote-data-all with other directives. However, it is recommended to place it anywhere in the file, except at the top, to avoid the issue described above.

Q: How can I report this issue to the Sphinx developers?

A: You can report this issue to the Sphinx developers by opening a new issue on the Sphinx GitHub page. Please include a detailed description of the issue, including any relevant code or configuration files.

Q: Is this issue specific to Sphinx or can it occur with other tools?

A: This issue is specific to Sphinx and is likely due to a bug in the doctestplus directive. However, similar issues may occur with other tools or directives that use similar syntax or functionality.

Q: Can I use a workaround to avoid this issue?

A: Yes, you can use a workaround to avoid this issue. One possible workaround is to place the doctest-remote-data-all directive after the first section or chapter in the RST file. This will ensure that the directive is processed correctly and does not cause Sphinx to crash.

Q: How can I ensure that my documentation is generated correctly?

A: To ensure that your documentation is generated correctly, you can use the following best practices:

  • Place the doctest-remote-data-all directive anywhere in the RST file, except at the top.
  • Use a consistent and well-structured RST file format.
  • Test your documentation regularly to ensure that it is generated correctly.
  • Report any issues or errors to the Sphinx developers or your documentation team.