Documentation build failure with sphinx 3.1

[xvitaly]

DefinitionError: Error when parsing function declaration:

  File "/usr/lib/python3.9/site-packages/sphinx/domains/cpp.py", line 6099, in _parse_type
    raise self._make_multi_error(prevErrors, header)
sphinx.util.cfamily.DefinitionError: Error when parsing function declaration.
If the function has no return type:
  Error in declarator or parameters-and-qualifiers
  Invalid C++ declaration: Expecting "(" in parameters-and-qualifiers. [error at 128]
    template<typename CompiledFormat, typename... Args, typename Char = typename CompiledFormat::char_type, CompiledFormat> ::value std::basic_string< Char > format (const CompiledFormat &cf, const Args &... args)
    --------------------------------------------------------------------------------------------------------------------------------^
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 154]
      template<typename CompiledFormat, typename... Args, typename Char = typename CompiledFormat::char_type, CompiledFormat> ::value std::basic_string< Char > format (const CompiledFormat &cf, const Args &... args)
      ----------------------------------------------------------------------------------------------------------------------------------------------------------^
  If declarator-id:
    Invalid C++ declaration: Expecting "(" in parameters-and-qualifiers. [error at 154]
      template<typename CompiledFormat, typename... Args, typename Char = typename CompiledFormat::char_type, CompiledFormat> ::value std::basic_string< Char > format (const CompiledFormat &cf, const Args &... args)
      ----------------------------------------------------------------------------------------------------------------------------------------------------------^
The full traceback has been saved in /tmp/sphinx-err-363v0ipx.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
Traceback (most recent call last):
  File "/builddir/build/BUILD/fmt-7.0.1/doc/build.py", line 72, in <module>
    build_docs(sys.argv[1])
  File "/builddir/build/BUILD/fmt-7.0.1/doc/build.py", line 53, in build_docs
    check_call([sphinx_build,
  File "/usr/lib64/python3.9/subprocess.py", line 373, in check_call
    raise CalledProcessError(retcode, cmd)

Sphinx-doc ticket: sphinx-doc/sphinx#8013

[xvitaly]

Doxygen issue: doxygen/doxygen#7927

[vitaut]

Thanks for reporting. This is annoying but doesn't affect the docs. Hopefully doxygen/doxygen#7927 will be fixed.