[Development] Supported compilers for Qt 6

[Lars Knoll]

> On 12 Aug 2019, at 10:54, Ville Voutilainen <ville.voutilainen at gmail.com> wrote:
> 
> On Mon, 12 Aug 2019 at 11:00, Lars Knoll <lars.knoll at qt.io> wrote:
>> 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).
> 
> Note that for GCC, 7 already has feature-wise almost everything for
> C++17. I have no problems with GCC 8 being the baseline,
> though; GCC 7 is already out-of-support from the upstream. Question
> about embedded targets (QNX, VxWorks, INTEGRITY):
> are we planning to indicate to the vendors of those platforms that the
> above gang-of-four-compilers is our baseline,
> and they need to achieve feature parity in order to be able to work with Qt 6?

Basically, yes. Qt 5.15 will be there and supported for the targets that do not have a decent enough toolchain (yet).
> 
>> 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.
> 
> We gain a slightly better baseline wrt. bugs; GCC for instance doesn't
> backport to closed branches, and GCC 7 is already
> closed, and 8 will follow relatively quickly. While we can't keep up
> with that during our (especially LTS) release cycle,
> at least we're not targetting already-obsolete versions too badly. :)

So I assume that’s a vote for the alternative proposal? :)
> 
>> So alternative proposal:
>> 
>> VC++ 2019
>> GCC 9
>> Clang 8
>> Apple Clang 11
> 
> Works for me.