[Development] Supported compilers for Qt 6

[Eike Ziller]

> On 12. Aug 2019, at 09:58, Lars Knoll <lars.knoll at qt.io> wrote:
> 
> 
> 
>> On 12 Aug 2019, at 09:45, Allan Sandfeld Jensen <kde at carewolf.com> wrote:
>> 
>> On Monday, 12 August 2019 09:17:58 CEST Lars Knoll wrote:
>>> Hi,
>>> 
>>> As mentioned in my blog, it would be good to move forward with the C++
>>> version we use for Qt 6 and ideally move it to C++17. That implies that we
>>> need to drop some older compilers for Qt 6. As 5.15 is going to be an LTS
>>> release, I don’t think this is going to be a huge problem.
>> 
>>> Here’s the baseline I would like to propose:
>>> 
>>> VC++ 2019
>>> GCC 8
>>> Clang 6
>>> Apple Clang 10.0
>>> 
>> Why not the latest for all the compilers, like gcc 9 and clang 8? I assumed we 
>> would use the 5.15 LTS to justify requiring the latest available compiler on 
>> all platforms.
> 
> I used the minimal version that seemed to be giving us decent C++17 support (according to https://en.cppreference.com/w/cpp/compiler_support). 
> 
> I’d personally be favour of using newer version of gcc/clang, but I’m not sure we gain a lot with it, as Apple clang is then probably the limiting factor. But we could upgrade that to Apple Clang 11 as well.
> 
> So alternative proposal:
> 
> VC++ 2019
> GCC 9

At least on CentOS / RHEL, GCC8 currently seems to be the latest available compiler (on CentOS/RHEL 7 via devtoolset-8). (No idea about timing of updated devtoolsets.)

> Clang 8
> Apple Clang 11
> 
>> 
>> Especially clang 6 is a bit old. 
> 
> Clang 6 is just a bit over a year old... :)
> 
>> I know for msvc-clang we already pretty much 
>> assume clang-cl 8. But we have not automated testing of non-apple clang, so it 
>> often breaks due to extra warnings or genuine clang bugs.
> 
> Yes. It would be good to have a build using standard clang in CI in the future. But that’s a separate topic :)
> 
> Cheers,
> Lars
> 
> 
> 
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Eike Ziller
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