PyQt6 build issues with GCC 16, related to operator!=

[Phil Thompson]

On 07/08/2026 22:57, Dmitry Shachnev wrote:
> Hi Phil!
> 
> With GCC 16.1 in Debian unstable, PyQt6 6.11.0 fails to build with this 
> error:
> 
>     QtCore/sipQtCorecmodule.cpp: In function ‘PyObject*
> slot_QLocale_Language___ne__(PyObject*, PyObject*)’:
>     QtCore/sipQtCorecmodule.cpp:8393:32: error: no matching function
> for call to ‘operator!=(QLocale::Language&, const QLocale&)’
>      8393 |             sipRes = operator!=(sipCpp, *a0);
>           |                      ~~~~~~~~~~^~~~~~~~~~~~~
>       * there are 2 candidates
>     In file included from
> /usr/include/x86_64-linux-gnu/qt6/QtCore/qcborvalue.h:9:
>         * candidate 1: ‘bool operator!=(QCborTag, QCborKnownTags)’
>           /usr/include/x86_64-linux-gnu/qt6/QtCore/qcborcommon.h:65:13:
>              65 | inline bool operator!=(QCborTag t, QCborKnownTags
> kt)   { return quint64(t) != quint64(kt); }
>                 |             ^~~~~~~~
>           * no known conversion for argument 1 from
> ‘QLocale::Language’ to ‘QCborTag’
>             
> /usr/include/x86_64-linux-gnu/qt6/QtCore/qcborcommon.h:65:33:
>                65 | inline bool operator!=(QCborTag t, QCborKnownTags
> kt)   { return quint64(t) != quint64(kt); }
>                   |                        ~~~~~~~~~^
>         * candidate 2: ‘bool operator!=(QCborKnownTags, QCborTag)’
>           /usr/include/x86_64-linux-gnu/qt6/QtCore/qcborcommon.h:66:13:
>              66 | inline bool operator!=(QCborKnownTags kt, QCborTag
> t)   { return quint64(t) != quint64(kt); }
>                 |             ^~~~~~~~
>           * no known conversion for argument 1 from
> ‘QLocale::Language’ to ‘QCborKnownTags’
>             
> /usr/include/x86_64-linux-gnu/qt6/QtCore/qcborcommon.h:66:39:
>                66 | inline bool operator!=(QCborKnownTags kt, QCborTag
> t)   { return quint64(t) != quint64(kt); }
>                   |                        ~~~~~~~~~~~~~~~^~
> 
> PyQt6-WebEngine 6.11.0 also fails to build with a similar error:
> 
>     QtWebEngineCore/sipQtWebEngineCoreQWebEngineFrame.cpp: In function
> 'PyObject* slot_QWebEngineFrame___ne__(PyObject*, PyObject*)':
>     QtWebEngineCore/sipQtWebEngineCoreQWebEngineFrame.cpp:458:22:
> error: 'operator!=' not defined
>       458 |             sipRes = operator!=((*sipCpp), *a0);
>           |                      ^~~~~~~~~~
> 
> This happens with SIP v6.15.3 and v6.16.0, with Python 3.13 and 3.14.
> Our Qt version is 6.10.2 at the moment.
> 
> I attached the generated sipQtCorecmodule.cpp for PyQt6, and I can 
> provide any
> additional information if you need it.

A C++ expert could probably help...

- the generated code has been working fine for years and years and still 
does with other compilers and older versions of GCC
- the problems only seem to be with operator!= and not operator==
- GCC v16 defaults to -std=c++20

The QLocale code expects the corresponding convertor ctor to be invoked 
automatically. I've changed the code (tonight's snapshot) to call the 
ctor explicitly - see if that improves things.

I am at a loss with the QWebEngineFrame code which doesn't use any 
implicit conversions. I've tried building with clang++ with -std=c++20 - 
no problems.

Phil