[Development] Proposal: Use -qt-zlib configuration in official MinGW builds

[Kai Koehne]

> -----Original Message-----
> From: Development [mailto:development-bounces+kai.koehne=qt.io at qt-
> project.org] On Behalf Of Konrad Rosenbaum
> Sent: Tuesday, November 29, 2016 11:03 AM
> To: development at qt-project.org
> Subject: Re: [Development] Proposal: Use -qt-zlib configuration in official
> MinGW builds
> 
> Hi,
> 
> On Monday 28 November 2016 17:11:19 Konstantin Tokarev wrote:
> > Currently, MinGW builds in Coin use -system-zlib configuration. It
> > happens because MinGW is shipped with zlib headers and libz.a.
> > However, linking zlib to several Qt modules (at least, QtCore, QtGui,
> > QtNetwork, and QtSvg) is suboptimal, while with -system-zlib one copy
> > in QtCore is shared between all modules.
> 
> Please be aware that there are quite a few Applications out there that use
> zlib independently of Qt - e.g. to encode/decode ZIP files. Unfortunately Qt
> does not expose its internal zlib headers, nor does it wrap all functionality of
> zlib. So at the very least qt-zlib needs to be linked in a way that allows an
> additional version of zlib to be linked.

This shouldn't be a problem, because the symbol ones from the internal version
are prefixed with "z_". See change 1f461ac45bf in qtbase.

Regards

Kai