[QGIS-Developer] Min qt version for 3.6?

[Nyall Dawson]

Hi list,

I'm wondering if we can bump the minimum Qt version for QGIS 3.6 to
something more modern, e.g. Qt 5.9.

The current minimum of 5.4/5.5 (no-one knows which it actually is!) is
very old, and very buggy. (See discussion at
https://github.com/qgis/QGIS/pull/8265). The sooner we can drop
support for 5.6, the better experience we can offer all round.

By bumping to 5.9 we'd lose support for Ubuntu 16.04, but I think this
is perfectly reasonable -- users of that platform would still be able
to run the QGIS 3.4 LTR release. (In my opinion, running an older LTR
distro should never equate to always having the latest end user
applications available.)

Would there be any objections to this change?

Nyall