[QGIS-Developer] QGIS 3.46 builds to use Qt6?

[Julien Cabieces]

> Nyall Dawson <nyall.dawson at gmail.com> writes:
>
>> On Tue, 17 Dec 2024 at 10:48, Greg Troxel via QGIS-Developer <
>> qgis-developer at lists.osgeo.org> wrote:
>>
>>> I wonder about "less stable" qt5 and "more stable" qt6.  Do we really
>>> believe that qgis built on qt6, with no plugins will have fewer crashes
>>> and quirks, than the qt5 build?
>>
>> Yes, I do. Because Qt 5 is not improving any more, but Qt 6 is. An example
>> would be when running under Wayland environments on linux -- it's a very
>> broken mess on Qt 5 and will never be fixed. On Qt 6 it's only a
>> slightly-broken mess, and will likely be non-broken within the next 12
>> months. There's a similar situation for apple processors, which never had
>> full official support on Qt 5 but ARE fully supported on Qt 6. This gap is
>> only getting wider as newer operating system updates and corresponding
>> changes break things underneath Qt 5.
>
>> There's also a limited stream of bug fixes getting ported back to Qt 5.15,
>> vs those flowing into the supported Qt 6 releases.
>
> That's a good argument.  I have not really dealt with qt6 yet, and my
> impression has been that qt5 is quite stable on my platform (which never
> had any official support).  But upstream's maintenenance policies are
> troubling.
>
>>>  That is surprising to me at this point.
>>> Do we still believe that if one assumes "qgis with N random plugins that
>>> claim to support qt6"?
>>
>> (Well, QGIS + **ANY** plugin = a less stable QGIS. 🤣 But that's a
>> completely different point)
>
> of course.  I just meant that stability(qgis-only) could have a
> different answer than stability(qgis+p1+p7), where p7 not working with
> qt6 leads to a 0 score on the stability metric.
>
>>> I expect a qt6 build is kind of like a .0 release, and we would want to
>>> have qt6 builds widel avaialable and time for feedback before saying
>>> it's stable.
>>
>> I'd say we're well past the ".0" stage of Qt 6 support. Almost all the core
>> functionality is quite well tested at this stage, and third party clients
>> (like Mergin and QField) switched to Qt 6 based QGIS builds earlier this
>> year. I'm confident that by the time we hit a (potential) October 2025
>> milestone that we'll have a very stable Qt 6 build available.
>
> My experience (not in qgis) is that broad releases often uncover
> problems not hit by testing with less scope.  Maybe there won't be much
> or perhaps even any, but until the broader qgis world, on varying
> systems.
>
> Therefore I think it would be good to start offering qt6 builds on the
> website before then, at least by July, to let a larger pool of users try
> them, marked "for testing" and then the labels can flip to "for use with
> old plugins"/"recommended".
>

Agreed, If we were to propose the 2 versions (Qt5 and Qt6) side by side,
we should propose the Qt 6 version for download sooner than october. Why not 3.42 in february?


>
> I will see about making the pkgsrc package have an option for which qt
> flavor, so I can test too.
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-- 

Julien Cabieces
Senior Developer at Oslandia
julien.cabieces at oslandia.com