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

[Greg Troxel]

Matthias Kuhn via QGIS-Developer <qgis-developer at lists.osgeo.org>
writes:

> A fixed date for releasing QGIS with Qt6 sounds like a good idea. And

I think it's important, as an open source project, to keep separate
concepts

  a) releases of source code, which can be built in various ways

  b) binary builds with specific options, for the convenience of users

I realize that many users care about (b), but packaging systems that use
(a), and open source needs to care about (a) as the logically important
thing.

> I am wondering if we are doing ourselves a favor if we continue to provide
> Qt5 builds after the shift.
> Wouldn't this prevent us from using pure Qt6 API's and bind development
> effort for backwards compatibility?

Providing category (b) binary builds is not the question.  It is
changing the source code to say that building with qt5 is no longer
supported.  (And really, to rip out qt5 support, because saying it isn't
supported while it works isn't a sensible plan.)

Perhaps that's what you meant, but it feels like "what can you build
from the source" and "what binary tarballs are on the website" are
commingled.

I see the transition as having multiple steps:

  Convince ourselves that building with qt6 is not a regression (absent
  plugin issues).  I think Nyall said we are already there.

  Make qt6 builds available for people that want to run them.

  Declare a timeline to plugin authors such that after some date, a
  plugin that does not have a released version that works with a
  qgis/qt6 build is broken and will be viewed as unmaintained.  (Plugins
  should arguably be marked as unmaintained if that's the case anyway;
  this label would appear on the qt5 version too.)

  Declare a process/timeline by which qgis will remove support for qt5, meaning
  that the sources will no longer build with qt5.  This might be "next
  branch won't".

  Declare a timeline to plugin authors when it is ok to remove support
  for qt5.

  After the qt6-required-plugin time arrives, document in README that
  packagers should use qt6 instead of qt5.  Label the qt6 builds on the
  website as preferred, viewing the website builds as the packaging
  system that it is.

  Decide not to worry about people running LTS systems that don't have
  qt6 but want new qgis.  Tell them that if they want to use old
  software, that the ilcenses grant them permission to do so, and wish
  them luck.

  Actually remove qt5 support from the sources.