[QGIS-Developer] QGIS and Qt 6: A proposal

[Nyall Dawson]

On Mon, 6 Jul 2020 at 23:21, Greg Troxel <gdt at lexort.com> wrote:
>
> Another thought is the spectre of "long term stable" OS releases.
>
> In various projects, I run into people who choose to run old software
> (otherwise known as "using a LTS distribution"), but at the same time
> insist on compiling the most recent release of X, and they expect X to
> build against old things.   I'm not a fan of this, but it seems to be a
> signficant part of Linux culture.

I also struggle with this mentality!

> So qgis will have to think about how long qgis will build:
>
>   against older qt5 stable branches (5.12?)

Unless there's a pressing reason to bump the qt dependency for 3.16,
I'd say we leave it unchanged for 3.16. That means we have a Qt 5.9
min requirement for the 5.16 LTR, which is extremely conservative.

>   against qt5 5.15

We would require all future QGIS 3.x versions to build on Qt 5.15 (and
probably earlier releases, say 5.11, unless there's a pressing need to
bump this after 3.16). And we drop this requirement in 2-3 years, when
it's time to start thinking about a new QGIS 4.0 major version where
we are allowed to break QGIS API.

Nyall