[Development] Installing Qt5Config.cmake from the Qt repo?

[lars.knoll at nokia.com]

Hi Stephen,

On 10/28/11 1:13 PM, "ext Stephen Kelly" <stephen.kelly at kdab.com> wrote:

>
>Hi,
>
>== Summary ==
>
>I'm considering adding some cmake files to Qt, which would be installed
>by Qt, 
>and which would make it easier for CMake based projects to depend on Qt.
>
>I'm CC'ing the cmake developers too see what they think of the idea too.
>
>== Clarification ==
>
>To avoid misunderstanding:
>
>* This proposal is not about porting the Qt build system to CMake.
>* This would not make Qt depend on CMake at all
>* I am proposing to add some plain text files to the Qt repo for
>installation
>* Those plain text files would need to be generated while building Qt
>(using 
>existing mechanisms, like perl).
>
>== How CMake finds packages ==
>
>(Skip this section if you already know how CMake finds packages)
>
>For those who have not used CMake before, it has two ways to find
>dependencies:
>
>* If you want to find a dependency, you write a Find<Package>.cmake file
>or use 
>    an existing one. Usually this Find<Package>.cmake will not be
>installed.
>
>* If you want to be easily found for others to depend on, you write a
>    <Package>Config.cmake file and install it to a location CMake will
>use to  
>    find things like that. I assume this is similar to how pkgconfig
>works, but 
>    I have never used pkgconfig.
>
>    This is most common in the case of projects which use CMake
>themselves, 
>    but there's no reason projects which do not use CMake can't provide
>    similar files. This becomes even more useful with recent CMake
>features 
>    based on finding packages.
>
>Either way, if someone does this in CMake:
>
>find_package(Package)
>
>the result is the ability to use the headers and libraries from Package.
>
>CMake ships with FindQt4.cmake, so anyone using CMake uses
>
>find_package(Qt4)
>
>to be able to use Qt 4.
>
>== Qt5Config.cmake ==
>
>I propose that we ship a Qt5Config.cmake file with Qt which we install,
>along 
>with macros equivalent to what is currently in Qt4Macros.cmake, and some
>Targets.cmake files.
>
>Then find_package(Qt5) in CMake would use that Config file and there
>would be no 
>need for a FindQt5.cmake.
>
>The advantage of this are:
>
>* It allows people using CMake to start experimenting with Qt 5 ports
>sooner
>* When new features arrive in Qt (such as new libraries like
>QtDeclarative was 
>in Qt 4) we can update the Qt5Config file immediately and test the new
>features 
>more easily.
>* We can use the cmake imported targets feature to more easily support
>debug 
>and release versions on Windows.
>* KDE does not need a separate FindQt.cmake to the one shipped by CMake.
>
>== Maintainance ==
>
>KDAB (specifically myself) can maintain these CMakes files. We have other
>engineers with both Qt and CMake competencies, and there are more people
>in 
>the CMake and KDE communities with cross-competencies.
>
>That is assuming it works of course. I haven't even prototyped yet in
>case 
>there is some reason this shouldn't be done. I'm quite confident it will
>work though.
>
>
>
>I can't think of any reason this effort should be prevented, but if you
>have a 
>reason, please let me know. I'm looking for early objections before I
>start to 
>do any work.

I think that's reasonable in general. It's similar to what we do to
support pkgconfig. I agree with Thiago's comment that this should be split
and we should have one file per shared library.

How is this dependency wise? Would we need to install these files into a
special location and how do we know where this location is? Does
supporting the feature require cmake to be installed?

Cheers,
Lars