[Development] Windows 7 support will be dropped in Qt 6

[Oliver Wolff]

Hi,

with Qt 6 approaching it is time to have a look at our set of supported 
platforms.

One candidate for removal of support was Windows 7. Some considerations 
about dropping this support have been communicated on Qt's development 
mailing list in March last year [1] and there were some discussions 
about this topic on the corresponding bug report [2]

The operating system was initially launched in 2009 and reached its 
official end of life in January 2020. That means that Microsoft no 
longer provides security updates and instances running Windows 7 should 
be replaced as soon as possible.

With this official Microsoft standing in mind our current plan is to 
remove support for Windows 7 in Qt 6.0 onwards. Qt 6.0 release is 
planned towards the end of 2020, roughly one year after Windows 7’s end 
of life.

Of course, we do not make decisions like this easily or to upset our 
users but there are clear advantages that speak in favor of dropping 
support:
     - We can rely on Windows functions being available instead of 
trying to dynamically load libraries which might or might not be available.
     - We can use functionality that only became available in later 
Windows versions unconditionally. One example of this can be UWP APIs 
which are Microsoft's "new way of writing APIs". Our new graphics 
abstraction (RHI) can also rely on newer features being available on 
Windows
     - We can focus our Windows resources on bug fixes and new 
functionality instead of maintaining this "legacy" operating system
     - CI resources that are used for Windows 7 tests can be used to 
test other configurations

Br, Olli


[1] 
https://lists.qt-project.org/pipermail/development/2019-March/035532.html
[2] https://bugreports.qt.io/browse/QTBUG-74687