[Development] Switching Qt default builds to C++20 where supported

[Fabian Kosmale]

Hi,

you've explicitly excluded ABI from the discussion ("Let's focus first on the C++ language, because
the ABI discussion is irrelevant if we don't do this"), and ignoring ABI, I do indeed see mostly two issues:

1. Ensuring that CI gives us enough test coverage, which I suspect might be solvable by configuring Qt  to build examples and tests by default still with 17.
2. Compile times, which I see getting worse when switching to 20, and not improving until we can use "import std". And that's not probably not viable even in C++23 builds unless mixing and matching of import and include of SLT headers works reliably. I don't consider compiles slower a blocker though, especially if compiling in 17 mode is still possible.


However, if it comes to ABI, I'm not convinced that we have a solution. As long as e.g. libstdc++ declares its support experimental, are we really willing to export C++20 symbols from Qt? If not, do we have strategy to prevent this from happening?

Kind regards,
Fabian


________________________________________
Von: Development <development-bounces at qt-project.org> im Auftrag von Thiago Macieira <thiago.macieira at intel.com>
Gesendet: Montag, 28. Oktober 2024 16:29
An: development at qt-project.org
Betreff: Re: [Development] Switching Qt default builds to C++20 where supported

On Monday 28 October 2024 00:59:25 Pacific Daylight Time Vladimir Minenko via
Development wrote:
> Hi Thiago,
>
> I would not take the silence as a sign of consent. I rather have the
> impression that there is no sufficient interest in this at the moment.
> Despite this, there are quite a few urgent improvements required on the CI.
> I greatly doubt it will be possible to have additional configurations for
> any of the permutations of conditions you might need.

Lazy consensus is part of our governance. If no one speaks up with arguments
against, it implies no one has arguments against of sufficient interest to them
to voice in the first place. Lack of interest and apathy imply people don't
care enough one way or the other.

I am not asking for additional configurations in the CI.

--
Thiago Macieira - thiago.macieira (AT) intel.com
  Principal Engineer - Intel DCAI Platform & System Engineering