Where to draw the line between Qt 4 and 5

[Mojca Miklavec]

Hi,

I would like to update Mercurial & TortoiseHG, but I don't know on
which OS Qt 5 may be declared as default one. Note that both Qt 4 and
5 work fine (see below), so it doesn't really matter which one is used
and I wouldn't want to break old OSes just because of a stupid
hardcoded requirement of Qt 5.

I don't want to make Qt 4 default on newer OSes either because it
doesn't work correctly on Retina display (many buggy issues with
scaling), but that's the last thing to worry about on 10.5.

I thought that maybe we should make Qt 5 default on darwin >= X, Qt 4
default on darwin < Y and potentially offer variants on Y <= darwin <
X and defaulting to Qt 4 (where we may set X = Y, making this subset
empty).

So: where should I draw the line? What should X/Y be?

The relevant PR is here:
    https://github.com/macports/macports-ports/pull/3664

Thank you,
    Mojca