[cmake-developers] Regression when using multiple Qt installations (FindQt4.make)

[Benoit Walter]

On Monday 07 May 2012, Clinton Stimpson wrote:
> On Sunday, May 06, 2012 04:27:17 am Benoit Walter wrote:
> > Hi CMake developers,
> >
> > as I need to maintain different projects using different Qt versions, I
> > needed to have a look at FindQt4.cmake.
> >
> > Based on the path of qmake, I can successfully decide which Qt version is
> > used (for example using Debian's update-alternatives).
> >
> > Ex:
> > /opt/qt4.7 (custom version)
> > /usr/include/qt4 (default version)PATH=/PATH=/path/to/custom/qt/bin:$PATH 
cmake ..path/to/custom/qt/bin:$PATH cmake ..
> >
> > However, even if I set qmake to the directory of the custom version, I
> > see that cmake uses the headers of the default version.
> >
> > It seems to me like a regression in commit
> > 0ae8a3405bb32afadda13f43100484e85f7ef74f ("Add qt4/QtCore to help find Qt
> > headers when cross-compiling.")
> >
> > qt4/QtCore is found in /usr/include instead of /opt/qt4.7/include, in
> > contradiction with the qmake information (qmake -query
> > QT_INSTALL_HEADERS).
> >
> > Corresponding lines in FindQt4.make:
> >       FIND_PATH(QT_QTCORE_INCLUDE_DIR QtCore
> >                 HINTS ${qt_headers} ${QT_LIBRARY_DIR}
> >                 PATH_SUFFIXES QtCore qt4/QtCore
> >         )
> >
> > Removing qt4/QtCore fixes the problem, but I guess that the commit was
> > useful for other reasons :)
> > So my suggestion is to either revert the commit because it invalidates a
> > common scenario when using cmake with several Qt installations, or to fix
> > the FIND_PATH call, making sure that the custom location is found before
> > the default one.
> >
> > Any idea?
> >
> > Best regards,
> > Benoit.
> 
> What version of cmake are you using?
> 
> I also have
> /usr/include/qt4
> and a custom Qt, but do not see this problem with the latest cmake.
> 
> The FIND_PATH(QT_QTCORE_INCLUDE_DIR QtCore
>                 HINTS ${qt_headers} ${QT_LIBRARY_DIR}
>                 PATH_SUFFIXES QtCore qt4/QtCore
> 
> It should first look for ${qt_headers}/QtCore, which should be
> /opt/qt4.7/include/QtCore.
> 
> I tried these 3 ways, but was not able to reproduce.
> 1. PATH=/path/to/custom/qt/bin:$PATH cmake ..
> 2. CMAKE_PREFIX_PATH=/path/to/custom/qt cmake ..
> 3. cmake ..  -> modify CMakeCache.txt to use custom qmake then re-run
>  cmake.
> 
> I have no "/usr/include" in my CMakeCache.txt file.
> 
> Can you expand the ${qt_headers} and tell me what you have?

I am using CMake 2.8.7. I would also expect that it first looks for 
${qt_headers}/QtCore and then qt4/QtCore but this is unfortunately not the 
case for me.

qt_header points to the right directory (/opt/qt4.7/include), so my guess is 
that the problem is related to the FIND_PATH() function. It seems that it 
first checks the default path (/usr/include). If I add the NO_DEFAULT_PATH 
argument, it works as expected and QT_QTCORE_INCLUDE_DIR points to the right 
directory (the custom one):

      FIND_PATH(QT_QTCORE_INCLUDE_DIR QtCore
                HINTS ${qt_headers} ${QT_LIBRARY_DIR}
                PATH_SUFFIXES QtCore qt4/QtCore
                NO_DEFAULT_PATH
               )

Maybe because of a recent CMake change in FIND_PATH()?

Note: On my system, the PATH is not changed (/usr/bin is *before* 
/opt/qt4.7/bin) and /usr/bin/cmake is linked to /opt/qt4.7/bin/cmake using 
update-alternatives. But that should not change anything and the first steps 
(including "_qt4_query_qmake(QT_INSTALL_HEADERS qt_headers)") are successful.

Regards,
Benoit.