[QGIS-Developer] When is Qt updated for the Windows releases?

[Nyall Dawson]

Hi all (well, mostly Jürgen),

I've been discussing with Nathan, and we have some questions about how
the Qt version library is handled with the windows builds, and when/if
we should be updating Qt libraries in our Windows releases.

If my understanding is correct, the osgeo4w architecture (and
correspondingly the windows release builds) only currently supports a
single version of qt 5 (and a single qt 4 version). If this is the
case, it means that upgrading our qt version at some stage to 5.9.4
(or 5.10.1) would also affect patch releases, right? E.g. updating to
5.10.1 for a future 3.2 release would mean that the next 3.0.x build
would also jump up to 5.10.1.

Is this interpretation correct? Do we consider this safe to do in a
patch mid-way through a stable release? And if not, does it mean we're
effectively stuck with the current version of Qt throughout the life
of 3.x?

I can't remember if we ever had to deal with this during 2.x - I'm
guessing we were probably stuck on the 4.8 ceiling from before we had
the whole LTR system in place (and maybe we've never had to deal with
this before).

Apart from https://issues.qgis.org/issues/17916 (which we need to
resolve before release anyway), there's some nice improvements in qt
5.10 which would be good to see us gain at some stage (notably the
much larger maximum QImage size -- opening the door for HUGE composer
outputs), and I'm sure the 3d engine is also much improved given the
heavy development there. So I'd hate to see the Windows builds locked
to 5.9 indefinitely.

Have you got any thoughts/plans for handling this situation? Keen to
hear your thoughts...

Nyall