[Docutils-develop] [docutils:bugs] #509 regression with docutils 0.22: unsupported operand type(s)

This looks like the problem reported in [bugs:508].

Could you check the Sphinx log?
Do you use "autodoc" or similar extensions to extract docstrings?


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**[bugs:#509] regression with docutils 0.22: unsupported operand type(s) for +: 'NoneType' and 'list'**

**Status:** open
**Created:** Wed Aug 06, 2025 06:13 PM UTC by Oliver Smith
**Last Updated:** Wed Aug 06, 2025 06:13 PM UTC
**Owner:** nobody


Hello,

after upgrading to docutils 0.22, building documentation for the pmbootstrap project fails:

~~~
    Traceback (most recent call last):
      File "/usr/lib/python3.12/site-packages/sphinx/cmd/build.py", line 432, in build_main
        app.build(args.force_all, args.filenames)
      File "/usr/lib/python3.12/site-packages/sphinx/application.py", line 426, in build
        self.builder.build_update()
      File "/usr/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 375, in build_update
        self.build(
      File "/usr/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 403, in build
        updated_docnames = set(self.read())
                               ^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 519, in read
        self._read_serial(docnames)
      File "/usr/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 584, in _read_serial
        self.read_doc(docname)
      File "/usr/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 648, in read_doc
        publisher.publish()
      File "/usr/lib/python3.12/site-packages/docutils/core.py", line 269, in publish
        self.document = self.reader.read(self.source, self.parser,
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/sphinx/io.py", line 103, in read
        self.parse()
      File "/usr/lib/python3.12/site-packages/docutils/readers/__init__.py", line 101, in parse
        self.parser.parse(self.input, document)
      File "/usr/lib/python3.12/site-packages/sphinx/parsers.py", line 86, in parse
        self.statemachine.run(inputlines, document, inliner=self.inliner)
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 165, in run
        results = StateMachineWS.run(self, input_lines, input_offset,
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/statemachine.py", line 235, in run
        context, next_state, result = self.check_line(
                                      ^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/statemachine.py", line 447, in check_line
        return method(match, context, next_state)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 2354, in explicit_markup
        nodelist, blank_finish = self.explicit_construct(match)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 2366, in explicit_construct
        return method(self, expmatch)
               ^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 2103, in directive
        return self.run_directive(
               ^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 2153, in run_directive
        result = directive_instance.run()
                 ^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/sphinxcontrib/autoprogram.py", line 262, in run
        nested_parse_with_titles(self.state, result, node)
      File "/usr/lib/python3.12/site-packages/sphinx/util/nodes.py", line 378, in nested_parse_with_titles
        ret = state.nested_parse(content, content_offset, node, match_titles=True)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 275, in nested_parse
        state_machine.run(block, input_offset, memo=self.memo,
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 191, in run
        results = StateMachineWS.run(self, input_lines, input_offset)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/statemachine.py", line 235, in run
        context, next_state, result = self.check_line(
                                      ^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/statemachine.py", line 447, in check_line
        return method(match, context, next_state)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 2787, in underline
        self.section(title, source, style, lineno - 1, messages)
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 321, in section
        self.new_subsection(title, lineno, messages)
      File "/usr/lib/python3.12/site-packages/docutils/parsers/rst/states.py", line 370, in new_subsection
        self.parent += section_node
      File "/usr/lib/python3.12/site-packages/docutils/nodes.py", line 736, in __radd__
        return other + self.children
               ~~~~~~^~~~~~~~~~~~~~~
    TypeError: unsupported operand type(s) for +: 'NoneType' and 'list'
~~~

Source code:
https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/

Tested with commit:
5927ff70b8d2468d5d0e2c978bc1fe30d036fd7f

Distribution:
Alpine Linux Edge


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