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

[Greg Troxel]

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.

A really big question is how packaging systems are going to deal with
qt6.  With qt4->qt5, pkgsrc had qt4 and qt5 packages.   qt4 remains,
although less and less uses it.   I am pretty sure some useful code that
uses qt5 is going to take a really long time to build against qt6, and
thus qt5 is likely to remain for several years.  This leads to needing
to have qt6 packages, rather than updating qt5 to "qt5-6.0.0".

I epxect Debian and Fedora are going to add qt6 that can be installed
alongside qt5, rather than just updating the qt5 packages to qt6,
because replacing qt5 with qt6 would lead to removing all qt5-using
packages  that don't have a release that works with qt6.  Certainly I
expect pkgsrc to head that way, and it would be interesting to hear from
Debian, FC, FreeBSD ports, the various mac-oly packaging systems, etc.