Raise minimum Qt version to 5.15.2

[glassez]

This is the last step on the way to compatibility of the code with Qt6.

[glassez]

@FranciscoPombal
Can you contribute into GHA CI part of it?

[FranciscoPombal]

@glassez

@FranciscoPombal
Can you contribute into GHA CI part of it?

Sure, done. glassez#2.

[glassez]

I think that it will not be a problem to merge this PR soon, since we are already using 3rd party Qt packages on Linux anyway, right?

[glassez]

I think that it will not be a problem to merge this PR soon, since we are already using 3rd party Qt packages on Linux anyway, right?

@Chocobo1
So, what kind of milestone would you assign for this PR? 4.4 or the next one?

[Chocobo1]

So, what kind of milestone would you assign for this PR? 4.4 or the next one?

I would chose 4.4.

[sledgehammer999]

IIRC from an older discussion, 4.4.x would supposedly target 5.14.x and around October (next Ubuntu release) we would bump to 5.15.x (and maybe release 4.5.x).

In the mainsite news I had left this:

Sunday May 2nd 2021 - qBittorrent v4.3.5 release

qBittorrent v4.3.5 was released.
This is the last release in the 4.3.x series. The next series will probably drop support for Ubuntu 20.04 (Focal Fossa) because the Qt5 version is too old now.

(intentionally blank line)

since we are already using 3rd party Qt packages on Linux anyway

No, the PPA builds use the OS's qt packages. I am in no position to re-package Qt and provide it via the PPA. I do it only for libtorrent.
If we bump to 5.15.2 the PPA will only support one Ubuntu version for now.

Will it be possible to maintain 5.14.2 for v4.4.x while master is at 5.15.2? (assume we can branch off v4.4.x now)

[glassez]

Will it be possible to maintain 5.14.2 for v4.4.x while master is at 5.15.2? (assume we can branch off v4.4.x now)

I think this shouldn't be a problem, apart from the fact that it will require manual commit picking from master to v4.4.x branch. But maybe then it makes sense to postpone it until v4.4.x stops following the master for other reasons (i.e. closer to v4.5 release)?

[FranciscoPombal]

@sledgehammer999

since we are already using 3rd party Qt packages on Linux anyway

No, the PPA builds use the OS's qt packages. I am in no position to re-package Qt and provide it via the PPA. I do it only for libtorrent.
If we bump to 5.15.2 the PPA will only support one Ubuntu version for now.

This (dropping support for older Ubuntu versions) was exactly the agreement we came to last time we discussed Ubuntu support. It simply moves too slowly. Also, soon another non-LTS Ubuntu release will come out which also has the necessary Qt support. 21.10.

The majority of users will be fine with staying on 4.3.x until 22.04 LTS rolls around. Those who really care can always install Qt themselves from the official distribution or a 3rd party PPA and compile from source.

Perhaps we should consider officially maintaining a flatpak to better support users on slow moving distros. This way, we could also stop maintaining the PPA version of libtorrent.

[sledgehammer999]

Also, soon another non-LTS Ubuntu release will come out which also has the necessary Qt support. 21.10.

This is a good point.
@glassez you can merge this if nothing else is pending.