[Development] Switch the main "Qt Build System"

[Thiago Macieira]

On Tuesday, 9 June 2020 23:07:55 PDT Bogdan Vatra via Development wrote:
> > The whole point of not bootstrapping the tools for cross compilation is to
> > remove as much as we can of the bootstrapping. Right now in 5.15, the only
> > tools that really need bootstrapping are qmake and moc. And for 6.0 once
> > the build system switch is merged, we can proceed to un-bootstrap qmake
> > too and that removes one full level of bootstrapping.
> > 
> > That will leave us with only moc needing bootstrapping. We can therefore
> > remove libQt5Bootstrap.a and minimise the amount of work needed to keep
> > the
> > bootstrap working.
> 
>   In this case why did you all had the super strict requirement list when we
> talked about using qbs as the build system for Qt 6? And why now you are so
> understanding and flexible with all the missing pieces from cmake?

I don't think I am being less strict. The strict requirement is that Qt does 
not require Qt for a non-cross-compilation. There has to be a starting point 
in the build chain. For a non-cross-compilation, there's a single build 
necessary; for a cross compilation, two and one of them could be minimal.

Clang can be compiled with GCC
GCC used to be compilable with other, Unix C compilers
GNU tar is packaged as a .shar file too
zlib used to be available as uncompressed .tar; now it has a .tar.xz

>   There are host tools that are not very forward or backward compatible
> (e.g. androiddeployqt) which might require a specific Qt version as it
> knows how to deal with a specific input files...

Those tools rely very much on internals *because* they've always been tied to 
a particular version, so people took liberties in writing those tools. Most 
should be updated so that they don't.

We don't have to fix this for 6.0.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel System Software Products