Compiling Subsurface against Qt in debug/developer mode

[Jan Mulder]

Currently, I'm (test) compiling Subsurface against the relatively new Qt 
5.10, which I compiled myself in developer mode. As the Qt source 
contains numerous asserts that are only active in developer mode, I 
(obviously) trip some of them while using our Subsurface (see for 
example, PR #977).

So, my question is now: what to do with this knowledge? When there is an 
obvious fix (like in 977), there seems no reason not to fix this in 
Subsurface. But now, I am stuck on a very deep down assert triggered by 
the new filter code. This code seems to work just fine in production 
code, and a fix on our side seems not straightforward. It might even be 
a bogus assert in Qt, or a bug in Qt.

So, another question: what do the Qt specialists here think of the 
"quality of the asserts in Qt source?". Are they of any use to non-Qt 
developers? Obviously, our main objective here is to improve Subsurface 
and not trying to debug Qt. That said, we might improve out code by 
assuming the Qt asserts are valid and correct, and improve our code not 
to trip those.

--jan