Infinite recursion when documenting PyO3 complex enums

Problem Description

pdoc enters infinite recursion when documenting extension modules created with PyO3 v0.28+, when the module
contains "complex enums" (Rust sum types translated into nested Python classes). The bug is only triggered when a .pyi typing stubs file is also present. The contents of this .pyi file does not matter, it may even be empty.

PyO3 v0.27 and earlier did not exhibit this behavior.

Steps to reproduce the behavior:

1. Build the PyO3 extension module containing "complex enums" with e.g. maturin develop. I've created a test extension module that is sufficient to reproduce the problem: pyo3-recursive-enum.
2. Try to generate HTML docs with pdoc -o html complex_enum.
3. RecursionError: maximum recursion depth exceeded exception is thrown.

Full backtrace:

Traceback (most recent call last):
  File "/home/raven/pyo3-recursive-enum/.venv/bin/pdoc", line 7, in <module>
    sys.exit(cli())
             ~~~^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/__main__.py", line 198, in cli
    pdoc.pdoc(
    ~~~~~~~~~^
        *opts.modules,
        ^^^^^^^^^^^^^^
        output_directory=opts.output_directory,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/__init__.py", line 548, in pdoc
    out = render.html_module(module, all_modules)
  File "/usr/lib/python3.14/contextlib.py", line 85, in inner
    return func(*args, **kwds)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/render.py", line 106, in html_module
    return env.get_template("module.html.jinja2").render(
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        module=module,
        ^^^^^^^^^^^^^^
    ...<7 lines>...
        mtime=mtime,
        ^^^^^^^^^^^^
    )
    ^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/jinja2/environment.py", line 1295, in render
    self.environment.handle_exception()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/jinja2/environment.py", line 942, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/templates/default/module.html.jinja2", line 315, in top-level template code
    {%- if loop.nextitem -%}
    ^^^^^^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/templates/default/frame.html.jinja2", line 36, in top-level template code
    {% block body %}
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/templates/default/frame.html.jinja2", line 40, in block 'body'
    <div>{% block nav %}{% endblock %}</div>
    ^^^^^^^^^^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/templates/default/module.html.jinja2", line 56, in block 'nav'
    {% block nav_members %}
    ^^^^^^^^^^^^^^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/templates/default/module.html.jinja2", line 57, in block 'nav_members'
    {% if module.members %}
    ^^^^^^^^^^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/jinja2/environment.py", line 490, in getattr
    return getattr(obj, attribute)
  File "/usr/lib/python3.14/functools.py", line 1126, in __get__
    val = self.func(instance)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc.py", line 342, in members
    doc_pyi.include_typeinfo_from_stub_files(self)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_pyi.py", line 140, in include_typeinfo_from_stub_files
    _prepare_module(module)
    ~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_pyi.py", line 81, in _prepare_module
    _prepare_module(member)
    ~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_pyi.py", line 81, in _prepare_module
    _prepare_module(member)
    ~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_pyi.py", line 81, in _prepare_module
    _prepare_module(member)
    ~~~~~~~~~~~~~~~^^^^^^^^
  [Previous line repeated 973 more times]
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_pyi.py", line 79, in _prepare_module
    for member in ns.members.values():
                  ^^^^^^^^^^
  File "/usr/lib/python3.14/functools.py", line 1126, in __get__
    val = self.func(instance)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc.py", line 261, in members
    for name, obj in self._member_objects.items():
                     ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/functools.py", line 1126, in __get__
    val = self.func(instance)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc.py", line 737, in _member_objects
    for name in self._var_docstrings:
                ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/functools.py", line 1126, in __get__
    val = self.func(instance)
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc.py", line 621, in _var_docstrings
    for name, docstr in doc_ast.walk_tree(cls).var_docstrings.items():
                        ~~~~~~~~~~~~~~~~~^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_ast.py", line 104, in walk_tree
    return _walk_tree(parse(obj))
                      ~~~~~^^^^^
  File "/home/raven/pyo3-recursive-enum/.venv/lib/python3.14/site-packages/pdoc/doc_ast.py", line 71, in parse
    src = get_source(obj)
RecursionError: maximum recursion depth exceeded

System Information

pdoc: 16.0.0
Python: 3.14.2
Platform: Linux-6.18.7-arch1-1-x86_64-with-glibc2.43

Reproduce the failure with the linked pyo3-recursive-enum extension, an accompanying .pyi file, and pdoc -o html complex_enum. Start in pdoc/doc_pyi.py at _prepare_module, then inspect pdoc/doc.py where members triggers stub processing. Done means documenting the PyO3 v0.28+ complex-enum module completes without RecursionError, including with an empty stub file.