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

[Volker Hilsheimer]

> On 28 Oct 2024, at 06:57, Thiago Macieira <thiago.macieira at intel.com> wrote:
> 
> On Friday 18 October 2024 08:36:22 Pacific Daylight Time Thiago Macieira wrote:
>> I'm going to assume that silence is consent to "there is no drawback" and
>> will proceed with the implementation.
> 
> It's been a week since I posted this, so as soon as I find the time to satisfy 
> the technical reviews, this is happening. The mailing list has spoken.
> 
> -- 
> Thiago Macieira


As long as we can guarantee that the binaries we distribute with this change are source- and binary-compatible with what is today released without this change, and as long as the other conclusions from the previous discussions hold (e.g. C++20 is not required, neither to build nor to use Qt), I’m not going to stop anyone from spending time on this.

I don’t know if and how we can guarantee that across all platforms. And, as Vladimir indicated: CI bandwidth is limited, and we will be prioritising that bandwidth for those configurations that we are going to support in the field, e.g. if in doubt and necessary, explicitly selecting C++17. Which might then just as well stay the default.

And sorry for not chipping things earlier. But frankly, C++ 20 has no priority for me, esp as long as the question on what substantial benefits this brings for our users (*not* to our developer experience) remains unanswered.

Volker