[Plplot-devel] Tentative plan for removing our support of Qt4

[Alan W. I. <Ala...@gm...>]

Hi António:

Your fix of the serious Qt5 font configuration bug for PLplot made our
Qt5 results in PLplot-5.15.0 essentially as good as our Qt4 results
for the first time ever.  So ever since that release it has been on my
mind to greatly reduce the complexity of our build-system *and*
testing of our Qt and PyQt components by only supporting Qt5 (i.e.,
dropping our support for Qt4).

The current build-system situation is Qt4 is looked for first, but if
it is not found Qt5 is used as a backup with the exception that Qt5 is
forced if the user specifies -DPLPLOT_USE_QT5=ON (which defaults to
OFF).  So my proposed plan to reach the above goal with minimum
disruption for users is the following:

* PLplot-5.16.0.  Use the exact same build system logic except that 4
   and 5 are swapped.  That is Qt5 is looked for first, but if it is
   not found Qt4 is used as a backup with the exception that Qt4 is
   forced if the user specifies -DPLPLOT_USE_QT4=ON (which defaults to
   OFF).  Warn in the release notes of this change and the
   corresponding replacement of the PLPLOT_USE_QT5 option with
   PLPLOT_USE_QT4 and also mention we plan to deprecate Qt4
   support in the next release and remove it in the next release
   after that.

* PLplot-5.17.0.  Deprecate Qt4, i.e., use it as a fall back from
   Qt5 *only* if the users sets -DPLPLOT_QT4=ON.  Warn in the release notes of
   this change and also warn we plan to remove support for Qt4 in
   the next release.

* PLplot-5.18.0.  Completely remove support for Qt4 which will finally achieve the
   desired simplifications mentioned above.

As someone here with a large familiarity with Qt, I would appreciate
you letting me know if you forsee any trouble with this overall plan
to remove our Qt4 support.  And comments on this plan from the other
PLplot developers here are also encouraged.

I will likely implement the 5.16.0 part of the above plan late this
week if there are no strong disagreements expressed here in the
next several days.

Alan
__________________________
Alan W. Irwin

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.org); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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Linux-powered Science
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