C++ domain: assertion failure in _resolve_xref_inner #14146
Description
Describe the bug
I'm trying to generate documentation for my project mxml but this fails due to an AssertionError. Log file is attached.
How to Reproduce
git clone https://github.com/mhekkel/mxml
cd mxml
cmake -B build -DMXML_BUILD_DOCUMENTATION=ON
cmake --buildEnvironment Information
Platform: linux; (Linux-6.12.57+deb13-amd64-x86_64-with-glibc2.41)
Python version: 3.13.5 (main, Jun 25 2025, 18:55:22) [GCC 14.2.0])
Python implementation: CPython
Sphinx version: 8.1.3
Docutils version: 0.21.2
Jinja2 version: 3.1.6
Pygments version: 2.18.0
Sphinx extensions
Additional context
# Platform: linux; (Linux-6.12.57+deb13-amd64-x86_64-with-glibc2.41)
# Sphinx version: 8.1.3
# Python version: 3.13.5 (CPython)
# Docutils version: 0.21.2
# Jinja2 version: 3.1.6
# Pygments version: 2.18.0
# Last messages:
#
# writing output... [ 85%]
# api/structmxml_1_1type__serializer
#
# writing output... [ 86%]
# api/structmxml_1_1value__serializer
#
# writing output... [ 87%]
# api/structmxml_1_1value__serializer_3_01T_01_4
#
# Loaded extensions:
# sphinx.ext.mathjax (8.1.3)
# alabaster (0.7.16)
# breathe (4.35.0)
# exhale (0.3.7)
# myst_parser (4.0.1)
# sphinxcontrib.jquery (4.1)
# sphinx_rtd_theme (unknown version)
# Traceback:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/sphinx/cmd/build.py", line 514, in build_main
app.build(args.force_all, args.filenames)
~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/application.py", line 380, in build
self.builder.build_update()
~~~~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib/python3/dist-packages/sphinx/builders/__init__.py", line 358, in build_update
self.build(
~~~~~~~~~~^
to_build,
^^^^^^^^^
summary=__('targets for %d source files that are out of date')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% len(to_build),
^^^^^^^^^^^^^^^^
)
^
File "/usr/lib/python3/dist-packages/sphinx/builders/__init__.py", line 437, in build
self.write(docnames, list(updated_docnames), method)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/builders/__init__.py", line 711, in write
self.write_documents(docnames)
~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/builders/__init__.py", line 725, in write_documents
self._write_serial(sorted_docnames)
~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/builders/__init__.py", line 741, in _write_serial
doctree = self.env.get_and_resolve_doctree(docname, self)
File "/usr/lib/python3/dist-packages/sphinx/environment/__init__.py", line 661, in get_and_resolve_doctree
self.apply_post_transforms(doctree, docname)
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/environment/__init__.py", line 729, in apply_post_transforms
transformer.apply_transforms()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib/python3/dist-packages/sphinx/transforms/__init__.py", line 94, in apply_transforms
super().apply_transforms() # type: ignore[misc]
~~~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib/python3/dist-packages/docutils/transforms/__init__.py", line 182, in apply_transforms
transform.apply(**kwargs)
~~~~~~~~~~~~~~~^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/transforms/post_transforms/__init__.py", line 44, in apply
self.run(**kwargs)
~~~~~~~~^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/transforms/post_transforms/__init__.py", line 90, in run
newnode = domain.resolve_xref(
self.env, refdoc, self.app.builder, typ, target, node, contnode
)
File "/usr/lib/python3/dist-packages/sphinx/domains/cpp/__init__.py", line 1111, in resolve_xref
return self._resolve_xref_inner(env, fromdocname, builder, typ,
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
target, node, contnode)[0]
^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/sphinx/domains/cpp/__init__.py", line 996, in _resolve_xref_inner
assert parentSymbol # should be there
^^^^^^^^^^^^
AssertionError