[CMake] speeding up FIND_PACKAGE(Qt4 ...)

[Andreas Pakulat]

Hi,

On Mon, May 7, 2012 at 10:00 PM, Miller Henry <MillerHenry at johndeere.com>wrote:

>
> We have a cmake based project where cmake runtime is becoming a problem:
> everytime a CMakeLists.txt changes the build takes an extra 40-50 seconds.
> Our main CMakeLists.txt contains a lot of ADD_SUBDIRECTORY (and little
> else).   Most of the subdirectories then call FIND_PACKAGE(Qt4) with
> various required components.  We have found that by moving this call into
> the top cmake we can save around 20 seconds.  However there is objection to
> doing this because some executables don’t need all the qt components.
> (In particular I object to linking QtTest into production code)
>
> Is there a way to do the Find package once, and then find individual
> components for link and include purposes separately?  Is there a better way
> so solve this problem?
>

One option would be to not use the QT_USE_FILE and instead have
target_link_libraries list all the Qt libraries individually. The
FindQt4.cmake module provides a variable for each Qt library it finds, so
you can decide for each target against which Qt components to link this
particular target.

Andreas
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