[Development] Proposing to officially allow C++20 types in Qt 6 ABIs

[Lars Knoll]

> On 28 Jan 2022, at 02:07, Thiago Macieira <thiago.macieira at intel.com> wrote:
> 
> On Thursday, 27 January 2022 16:49:22 PST Marc Mutz wrote:
>> That would break projects that build their Qt themselves (embedded), and
>> with C++17 (because, you know, compile times increase with every std
>> version 🙂).
> 
> Ok, then we make it optional to turn back the clock and compile as C++17. But 
> we default to C++20. This option would be as ABI-breaking as the feature 
> system or choosing qreal == float. 

I’d be fine with that given that we have good enough C++20 support on the desktop and mobile platforms. We upgrade the default to C++20, but keep things compiling in C++17 mode. If we do that, we should however consider upgrading our minimum compiler requirements for the binaries (ie desktop and mobile platforms) to compilers that support C++20. In addition, we’ll need to add testing of C++17 builds in CI.

The last question is whether we would do that switch for 6.4 or 6.5.

Cheers,
Lars