[Development] Supported compilers for Qt 6

[Ville Voutilainen]

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?

> 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 alternative proposal:
>
> VC++ 2019
> GCC 9
> Clang 8
> Apple Clang 11

Works for me.