[Development] Did we have to remove cmake's qt5_use_modules?

[qt.dantec at free.fr]

Le Wed, 06 Jun 2018 23:03:40 -0700, Thiago Macieira
<thiago.macieira at intel.com>  écrivait:

>But it appears that in the 5 years since we deprecated it, people have not 
>stopped using it. Did we have to remove it? Or should we have kept 
>compatibility until Qt 6?

The Qt promise is to maintain not only source code, but upward binary
compatibility until a major version.

When said promise is broken immediately after a major version release,
as it was the case just after Qt5 release to fix an oversight, this is
not harmful.

When it happens years after release, and this is indeed the case here
for deprecated modules, and was also the case with the switch away
from Webkit, it can be a major problem not just for distributions, but
for many projects that depend on it and did not budget a major change.

To maintain source and binary compatibility, deprecated modules should
not be removed until QT6. I do not even understand why there is a
debate about this.