[webkit-dev] Moving away from qmake

[Oliver Dole]

Hello,

Here is my experience with cmake, so I hope it may help you to decide
which build system is the best for you.
Its first advantage is that it is cross platform. So you can imagine
in a long term approach to have a unified build system between
GTK/Qt/Wx/Win and mac.
Another advantage is that it is from my point of view quite simple to
understand and to use for basic stuff like adding a library dependency
to the build. Moreover there are many ready to use macro to ease this
work. As an example, if you want to add a dependency with JPEG
library, use FindJPEG module and it will store useful info in
variables like JPEG_LIBRARIES.
About documentation, well simply have a look at
http://www.cmake.org/HTML/Documentation.html page, it should convince
you.
Another feature I like are curses interfaces for your project
configuration (you can switch options, compiler flags and even
compiler). And of course you do not have to rebuild the whole project
each time you modify things. And if things are done correctly you do
not even have to rebuild the whole project when you add a new feature.
Imagine that you have built WebKit/GTK without SVG support and you
want to add it. It can simply recompile svg missing .o and of course
redo linking. Of course that's not true if you switch from a debug
build option to a release build.
Of course from time to time you may have to rebuild the whole project
because you have modify things in cmake config files.
Another insteresting features is that cmake allow you to create a
build directory where will be stored all your object files. So your
source tree remains clean.
About drawbacks, the main is about cross-compilation. I know that
cmake guys work on this issue but currently I still have to do ugly
things when I cross compile webkit because of dftables. As a matter of
fact dftables is also cross-compiled and when you try to run an ARM
dftables exec on a x86 arch, it cannot work. But I hope I will be able
to fix this soon. The more people are involved in Cmake process, the
more we get chances to overcome these little issues.
The other drawback you can have is that you will have to
compile/install cmake when you are in a scratchbox environment.
And if you want to give a try to cmake alternative, let me know, I can
provide you files to compile WebCore/JavascriptCore with cmake. And I
can also try to help you to meet your goal.

Regards,

> De : Alp Toker <alp at atoker.com>
> Date : 12 novembre 2007 04:34:48 HNEC
> À : webkit-dev at lists.macosforge.org
> Objet : [webkit-dev] Moving away from qmake
>
>  The existing qmake-based build system is shared by the GTK+ and Qt ports.
>
> Until recently, this arrangement has not been too problematic for the
> GTK+ porters, with the idea being that qmake makes life easier for
> developers at the expense of a little inconvenience for users (in the
> sense of application developers rather than end users).
>
> However, it has recently become clear that qmake is actually making life
> more difficult for developers. It turns out that the existing qmake
> build system fails to do basic dependency tracking, leaving both
> developers and users with crashy builds, with the only way to get a
> stable build being to do a full clean and rebuild after every update.
>
> In the last week I've had to explain why people's builds are crashing to
> maybe half a dozen people on WebKit and GNOME-related channels.
>
> Mark and I have attempted to fix the dependency tracking a number of
> times, but we've both found qmake to be poorly documented, and our
> attempts to fix it ended up breaking the build even more in certain
> configurations. My informal attempts to get assistance from the
> Trolltech guys doing the Qt port have gone unanswered. I have no doubt
> that we would be able to fix these issues in a matter of minutes using a
> better understood or documented build system.
>
> Moreover, it has turned out that the qmake build dependency is more than
> just a little inconvenience for users. It makes the GTK+ port
> inaccessible to a lot of developers. Using anything but the latest Linux
> distributions, including cross-compilation frameworks like Scratchbox,
> you have to build the whole of Qt just to get qmake, which takes over an
> hour and almost a gigabyte of disk space for me. That's at least 5 times
> as long as it takes to build the whole of JavaScriptCore, WebCore and
> WebKit. Even in distributions that ship a recent binary of qmake, it is
> often bundled into the same binary package as the rest of Qt, making it
> a seriously large dependency.
>
> Now that the GTK+ port is getting attention from beyond a core team of
> developers, I think such a heavy build dependency is no longer acceptable.
>
>
> If either the Wx or Qt porters are willing to share a new build system
> with the GTK+ port, they should speak up now. We're willing to consider
> any build system that does not incur a huge dependency (ruling out
> qmake) and that is actively maintained and does not have verbose XML
> makefiles (ruling out Bakefile and Ant-like build systems respectively).
> cmake and autotools are fair game here, for example.
>
> If we cannot reach a conclusion, the GTK+ port will most likely go ahead
> and switch to autotools. Work has already started to provide an
> autotools-based build system at
> http://git.ndesk.org/?p=javascriptcore-modular
>
> An unforeseen benefit of the new build system is that it is modular,
> rather than monolithic, and has no dependency on GLib/GTK+ or any other
> framework. This means that it will now be possible to use JavaScriptCore
> as a standalone scripting engine independently of WebKit.
>
>
> I hope I've accurately summarised the thoughts of all those involved here.
>
> (It's quite unfortunate that we might end up contributing to the current
> proliferation of build systems, but I think it's fair to say that the
> qmake dependency is right now the biggest single issue holding back
> development and acceptance of the GTK+ port. If other ports are willing
> to compromise in the same way as we are on a shared solution, this
> proliferation can still be avoided.)
>
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-- 
Olivier DOLE
Pleyo
Software Engineer