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

[Clinton Stimpson]

On Monday, May 07, 2012 08:43:07 am Benoit Walter wrote:
> 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.

According to the docs, /usr/include is searched after any paths given by 
HINTS.  However, I can reproduce your problem by doing this:
export CMAKE_PREFIX_PATH=/usr
cmake -DQT_QMAKE_EXECUTABLE=/path/to/custom/qt/bin/qmake ../

but that can easily be fixed by a more standard approach of specifying a 
desired package (in this case, Qt) in CMAKE_PREFIX_PATH instead.
export CMAKE_PREFIX_PATH=/path/to/qt:/usr
cmake ../

So, are you setting either CMAKE_PREFIX_PATH or CMAKE_INCLUDE_PATH in the 
environment or in your CMakeLists.txt files?

-- 
Clinton Stimpson
Elemental Technologies, Inc
Computational Simulation Software, LLC
www.csimsoft.com