[Development] Proposing CMake as build tool for Qt 6

Jean-Michaël Celerier jeanmichael.celerier at gmail.com
Mon Jun 17 13:05:41 CEST 2019

> The world is not spinning around Qt, sorry for the bad news.

On that we agree : https://www.jetbrains.com/lp/devecosystem-2019/cpp/
I mean, I had actual CMake classes with a CMake exam on paper 6 years ago
at the university -- you get a few hundreds of new devs on the job market
every year out of that one, who *will* know CMake, and won't know qmake /
qbs / [...].

> I prefer a transparent self-bootstrapped Qt over an explicit two stages

I (entirely personnally) really do not, - this is anecdotally one of the
main objections I've heard about Qt (3k questions just about Qt's configure
in SO ! https://stackoverflow.com/search?q=%5Bqt%5D+configure) : not just
answering to a standard cmake && make && make install which comes with gui
discoverability through cmake-gui, embeddability through add_subdirectory
or C++ package managers such as conan, vcpkg, hunter, etc etc. but instead
acting like its own microcosm library where you have to learn yet another
set of commands & invocations if you want to integrate it in your existing

> Last comment: Please think about [...] Cmake is not yet ready for that.

> embedded Linux
Oh come on.

> qnx
you mean like software companies using Qt do, today ?

> vxworx

VxWorks ships with CMake so there must be at least some amount of support. (

> iOS

... yes ? https://github.com/sheldonth/ios-cmake
Also, just because CMake now has acquired *official* support for iOS does
not mean that it hasn't been working for a long time. There were people
shipping iOS apps with CMake five years ago - and this is due in part to
CMake having a *large* community, unlike qmake / qbs, which means that even
if CMake does not directly support $FEATURE, chances are that you can find
an aptly-licensed open-source library that you can use to augment your
build with and achieve what you want.
See e.g. all the projects that ship today with
https://github.com/leetal/ios-cmake, https://github.com/ruslo/polly, etc
In contrast, how many people are shipping qmake extensions outside of
QtCore, as a library for anyone to use ?

> android and whatever next os is coming.
Oh come on (bis). CMake has been one of the official android build systems
for close to two years now : https://developer.android.com/ndk/guides/cmake

Also, C++Builder was able to ship and advertise CMake support for Android &
iOS a year ago so there is no reason Qt cannot do the same :

> and whatever next os is coming.

you mean like Fuschia (
or maybe actual operating systems built with CMake, such as IncludeOS (
https://github.com/includeos/IncludeOS) or ReactOS (
https://github.com/reactos/reactos) ? :-)


On Mon, Jun 17, 2019 at 11:05 AM Christian Gagneraud <chgans at gmail.com>

> On Mon, 17 Jun 2019, 20:15 Elvis Stansvik, <elvstone at gmail.com> wrote:
>> Den mån 17 juni 2019 kl 09:12 skrev Christian Gagneraud <chgans at gmail.com
>> >:
>> >
>> > On Mon, 17 Jun 2019, 18:11 Jedrzej Nowacki, <Jedrzej.Nowacki at qt.io>
>> wrote:
>> >>
>> >> On Saturday, June 15, 2019 6:37:24 PM CEST Thiago Macieira wrote:
>> >> > On Saturday, 15 June 2019 02:18:28 PDT Jean-Michaël Celerier wrote:
>> >> > > You can download a CMake static binary (
>> https://cmake.org/download/) that
>> >> >
>> >> > (...)
>> >> >
>> >> > I would prefer that our requirements be present in Linux
>> distributions we
>> >> > declare are supported build environments. If nothing else, our CI
>> will
>> >> > benefit from this.
>> >>
>> >> Let's not pull CI into it. It already
>> >
>> >
>> > Wow! Let's not pull in the system which only goal is to validate the
>> "supported platforms" promise, is it what you mean?
>> > If I need a special cmake to build Qt, then this should be shipped as
>> part of Qt itself, another third-party source tree.
>> > And then it means that I will need to build qt's build system. In other
>> words, I'll have to bootstrap Qt build system.
>> > I thought that it was a big no-no. The main argument to ditch qmake and
>> qbs...
>> Hm, what is the problem with using the official CMake binaries? Isn't
>> that what you'd do on Windows / macOS anyway?
> In case you didn't follow the thread, building Qt with cmake requires a
> non-released version of cmake.
> The question is:
> By the time qt6 will be out, will the requirement of cmake minimum version
> be met by, say, the latest (two) Ubuntu LTS release? (Or Macos, ...)
> The answer is that, best case, this is doable if qt6 is not released
> before 2022 or 2024. (Current req. Is unreleased cmake 2.15. assuming the
> minimum req. is not bumped, which is very unlikely given the lack of
> support for Android, iOS, etc...)
>> If distro X (e.g. *buntu 20.04) happen to ship a sufficient version
>> when it arrives, then great. But having to install the build tool from
>> the vendor instead of the distro package manager surely can't be a
>> blocker
> Really? Then convince the boot2qt team to force yocto to use the latest
> bleeding edge cmake version for their stable branch...
> Good luck with that.
> And then, which is my point, you're asking your customers to build/install
> Qt build system in order to build Qt itself.
> That is wrong. The world is not spinning around Qt, sorry for the bad news.
> I prefer a transparent self-bootstrapped Qt over an explicit two stages
> one.
> Right now the cmake build system doesn't respect the initial requirements
> that were used to ditch contenders.
> This is in no way a democratic process.
> This is selective hearing, reqs for cmake are artificially lowered while
> reqs for contenders are artificially raised.
> I have no doubt that cmake will be Qt6 build system, this is your choice,
> I'm just asking to stop this simulation, and I'm asking you to take your
> responsibilities, if building Qt6 is not supported on mainstream platforms
> I might consider switching away from Qt.
> Last comment: Please think about embedded Linux, qnx, vxworx, iOS, android
> and whatever next os is coming.
> Cmake is not yet ready for that.
> Chris
>> Elvis
>> >
>> > Chris
>> >
>> >
>> >> covers installation of the cmake in
>> >> order to test wip/cmake branch (
>> https://code.qt.io/cgit/qt/qt5.git/tree/coin/
>> >> provisioning/common/linux/cmake_linux.sh?h=wip/cmake)
>> >>
>> >> Cheers,
>> >>   Jędrek
>> >>
>> >>
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