[QGIS-Developer] [Qgis-psc] How to handle upstream Qt fixes

[Peter Petrik]

Hi,

as for macOS at the moment, I install pre-build Qt binaries and use them. I
suppose I can build and use whichever version from whichever fork if we
decide to do so, but I have never needed to use my custom Qt build so it
would take some time to compile.

as for Qt and their (lack of) open-source support for 5.15, I am wondering
if they want to force open-source projects to use a commercial Qt package
for distribution?

P.

On Mon, Sep 6, 2021 at 1:06 AM Nyall Dawson <nyall.dawson at gmail.com> wrote:

> On Sat, 4 Sept 2021 at 17:56, Richard Duivenvoorde <rdmailings at duif.net>
> wrote:
> >
> > On 9/4/21 8:45 AM, Ludovic Hirlimann wrote:
> > > On 9/3/21 00:46, Nyall Dawson wrote:
> > >> Hi PSC, devs,
> > >>
> > >> I'd like to kick start some discussion on how best to handle the
> > >> situation with upstream Qt and their (lack of) support for Qt 5. As a
> > >> quick summary of the situation:
> > >>
> > >> - Qt Co effectively ended open source support of Qt 5 at the 5.15.2
> > >> release, and have moved all focus to Qt 6.
> > >> - While some preliminary work has been done, QGIS doesn't currently
> > >> support Qt 6 based builds, and likely won't be ready for this for some
> > >> time (even completely ignoring all the stable API questions a Qt 6
> > >> build raises entirely!)
> > >
> > > Wouldn't it be wiser to devote resources to moving to QT6 and do that
> faster than
> > >
> > > wait on potential unsuported 5x fixes ?
> >
> > That was also my thought, though no clue about the amount of work for it.
> >
> > But my argument against deciding to use a patched/forked qt5 would be
> that (UNLESS all our development platforms could more or less
> easily/package/use it), it could potentially break our (little?) "I'm not a
> core dev, but I compile QGIS myself" group.
> >
> > My experience (with Linux users at least), is that with some guidance
> the average Debian/Ubuntu user is able to compile/run QGIS itself, IF all
> dependencies are taken care of by the distro's.
> > When people have to fiddle with LD_LIBRARY paths, my guess is they will
> break...
> > Off course that is 'my bubble', and I'm not even sure about the size of
> the group, and if they/we are helpful at all etc etc.
>
> I'd never make the KDE fork a requirement for a bulid -- we'd always
> have to ensure that users can build using the official releases.
> They'd just potentially suffer from upstream Qt bugs which have since
> been fixed in the community fork. (And if we do nothing, they'd be in
> exactly the same situation!!)
>
> > Maybe it's time for another 'big gap' in QGIS releases? As in: after
> 3.22 (LTR) there will be a probably not so stable 4.0 which will have a
> thorough api cleanup (first), while maybe partially trying to do some
> pre-work for Qt6? And so hopefully we will have Qt6 packaged more easily at
> that time?
>
> See https://github.com/qgis/QGIS-Enhancement-Proposals/issues/198 for
> my proposal on how we handle this. I'd suggest that (when we're ready)
> we do a "soft break" and support Qt 6 builds of QGIS 3.x, with the
> intention of moving the Windows and Mac builds to Qt 6. We don't allow
> ANY api breaks which aren't directly related to making QGIS qt6
> compatible, so that plugins will only have to make very minimal
> changes (if any)
>
> > What is the Qt6 status in Fedora or Suse?
>
> Fedora has qt 6.1 packages from Fedora 34 (we use these on the CI to
> test builds of the core/analysis library on Qt 6). Not sure about SUSE
> personally.
>
> Nyall
>
>
> >
> > Glad to see Riverbank at least has PyQt6 already.. (and yes I'm aware Qt
> now also has bindings itself :-) )
> >
> > Anyway, thanks Nyall for this forward thinking, but ... hard decisions
> to make. ...
> >
> > May the QGIS Force be with us...,
> >
> > Richard Duivenvoorde
> >
> > [0] https://tracker.debian.org/pkg/qtbase-opensource-src
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