Using Unicode identifiers in C++ fails #14026
Description
Describe the bug
Repost of breathe-doc/breathe#1044, since I suspect the underlying issue is in Sphinx itself:
Thanks for this nice package!
I have attached a MWE: test-doc.tar.gz, as well as a minimal index.rst.
In short, using Unicode identifiers fails, as in this example:
/**
@brief My very own struct.
*/
template<typename T>
struct MyStruct {
T α; ///< A magic number
};
namespace my_namespace {
/**
@brief Print the value of `ξ`.
@param ξ The value to be printed.
*/
void my_fancy_function(int ξ) {
std::cout << "ξ = " << ξ << std::endl;
}
}The error message I am getting:
/private/tmp/test-doc/index.rst:18: WARNING: Error in declarator or parameters-and-qualifiers
If pointer to member declarator:
Invalid C++ declaration: Expected identifier in nested name. [error at 2]
T α
--^
If declarator-id:
Invalid C++ declaration: Expected identifier in nested name. [error at 2]
T α
--^
/private/tmp/test-doc/index.rst:20: WARNING: doxygenfunction: Unable to resolve function "my_fancy_function" with arguments "None".
Candidate function could not be parsed. Parsing error is
Error when parsing function declaration.
If the function has no return type:
Error in declarator or parameters-and-qualifiers
Invalid C++ declaration: Expected identifier in nested name, got keyword: void [error at 4]
void my_fancy_function (int ξ)
----^
If the function has a return type:
Error in declarator or parameters-and-qualifiers
If pointer to member declarator:
Invalid C++ declaration: Expected '::' in pointer to member (function). [error at 23]
void my_fancy_function (int ξ)
-----------------------^
If declarator-id:
Invalid C++ declaration: Expecting "," or ")" in parameters-and-qualifiers, got "ξ". [error at 28]
void my_fancy_function (int ξ)
----------------------------^ [docutils]
and the resulting output:
Meanwhile, the Doxygen HTML output works fine:
If I replace the Greek letters with Latin identifiers, the documentation builds correctly.
How to Reproduce
Simply run make in the extracted folder of the attached MWE test-doc.tar.gz
For an absolute minimum index.rst, that reproduces the error:
.. TestDoc documentation master file, created by
sphinx-quickstart on Tue Nov 4 08:08:50 2025.
You can adapt this file completely to your liking, but it should at least
contain the root `toctree` directive.
TestDoc documentation
=====================
Add your content using ``reStructuredText`` syntax. See the
`reStructuredText <https://www.sphinx-doc.org/en/master/usage/restructuredtext/index.html>`_
documentation for details.
.. toctree::
:maxdepth: 2
:caption: Contents:
.. cpp:function:: void my_fancy_function(int ξ)
Print the value of ξ.
.. cpp:var:: ξ
The value to be printed.
.. cpp:struct:: template<typename T> MyStruct
My very own struct
.. cpp:member:: T α
A magic numberEnvironment Information
Platform: darwin; (macOS-26.0.1-arm64-arm-64bit-Mach-O)
Python version: 3.14.0 (main, Oct 7 2025, 09:34:52) [Clang 17.0.0 (clang-1700.3.19.1)])
Python implementation: CPython
Sphinx version: 8.2.3
Docutils version: 0.21.2
Jinja2 version: 3.1.6
Pygments version: 2.19.2
The virtual environment was instantiated from the following `requirements.txt`:
sphinx>=8,<9
breathe
sphinxcontrib-bibtex
furo
Sphinx extensions
Only extension I use is "breathe".Additional context
No response