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

[Greg Troxel]

Nyall Dawson <nyall.dawson at gmail.com> writes:

> On Mon, 6 Jul 2020 at 22:38, Greg Troxel <gdt at lexort.com> wrote:
>>
>> Bo Victor Thomsen <bo.victor.thomsen at gmail.com> writes:
>>
>> > 3. I like the idea, that you can build QGIS with both the QT ver 5.x
>> >    and QT ver 6.x in a (limited) time period. That gives the plugin
>> >    developer some peace of mind, having both the "old" and the "new"
>> >    QGIS as a testing ground before plugin release
>>
>> I like this too, but given many packaging systems and many reasons, I
>> see "limited" as being like a year and maybe more.  Basically it would
>> be nice if qgis worked on both until very few people had a reason to use
>> qt5, and I think that just means  sticking to the non-deprecated API in
>> 5.15.
>
> Actually I'd be perfectly fine if we start adding new features which
> rely on functionality added in Qt 6, so long as these are
> automatically disabled on the Qt 5 builds. We have precedent for this
> in the past -- when QGIS 3D was introduced it was only available if
> the Qt library version was sufficiently recent, and also when GeoPDF
> export was added we only enabled it for GDAL 3 builds.

That's fine with me from the packager perspective.  I wasn't thinking
about new features that are "#ifdef QT6".  I indeed meant not moving
existing things to require qt6.

Basically packaging systems get forced into choices by various things
and end up not being able to satisfy all of them.  So as long as qgis
still builds with 5.15 and that remains at least a mostly reasonable
choice for a while, that's fine.