[Development] Proposing CMake as build tool for Qt 6

Jean-Michaël Celerier jeanmichael.celerier at gmail.com
Wed Jun 12 09:21:26 CEST 2019


Even if modules were available (and stable) in at least mainline versions
of {clang, gcc, msvc} in a year (which I don't think they will), Qt would
have to get modularized to actually be able to reap the benefits of modules
(given the strong feelings in the "deprecations" thread, we can expect
mid-2050 for that one maybe ? e.g. for now Qt 6 will be AFAIK on a C++17
baseline... if we consider that it took up to Qt 5.7, released in 2016, to
require a C++11 compiler to build, you can see that `import QString;` in
qobject.h is still a decade away :-)).

So I really think that the time saved by PCH today, which is for me at
least a good few minutes per Qt build, is important to keep.
Besides, current implementations of modules aren't faster than a good PCH
(or at least they weren't last time I checked clang's).

Best,
Jean-Michaël

On Tue, Jun 11, 2019 at 5:50 PM Matthew Woehlke <mwoehlke.floss at gmail.com>
wrote:

> On 06/06/2019 09.23, Simon Hausmann wrote:
> > Regarding PCH, it seems that right now it would be easiest to
> > include something like https://github.com/sakra/cotire . Patches are
> > welcome to integrate this or alternatively work with upstream CMake
> > for a built-in solution.
>
> Considering that modules are coming, I wonder how much sense it makes to
> keep working on PCH?
>
> --
> Matthew
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