[cmake-developers] Generating imported library targets without the cmake executable

[Stephen Kelly]

Hi there,

I am working on installing CMake config files from the Qt repository so that 
there is less need for a FindQt.cmake. 

The motivation is that between releases of Qt and CMake, the features of Qt 
get out of sync with the features available through FindQt.cmake, but with 
config files that is not the case. Additionally, as the Qt buildsystem knows 
everything about the package it is creating, it is possible to create config 
files that already 'know the answers' and locations of everything without 
having to find+query.

The previous discussion on this is here:

http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/2090

the current candidate for inclusion in Qt is here (which requires an account 
in the Qt jira):

http://codereview.qt-project.org/#change,8518

and here (which does not): 

https://qt.gitorious.org/+kdab-developers/qt/kdab-developers-
qtbase/commit/913fd3a1acffbae2ca8f6967dd951a03ff9f76a4

There is a small sticking point to this being in a finished state:

In creating the imported targets, I attempt to create the same content as 
cmake creates when using install(EXPORTS). So I generate something along 
these lines:

get_filename_component(_qt5_install_prefix 
                       ${CMAKE_CURRENT_LIST_DIR}/../../../ ABSOLUTE)

set_property(TARGET Qt5Core APPEND PROPERTY IMPORTED_CONFIGURATIONS DEBUG)
set_target_properties(Qt5Core PROPERTIES
    IMPORTED_LINK_INTERFACE_LIBRARIES_DEBUG ""
    IMPORTED_LOCATION_DEBUG "${_qt5_install_prefix}/lib/libQtCore.so.5.0.0"
    IMPORTED_SONAME_DEBUG "libQtCore.so.5"
)

set_property(TARGET Qt5Core APPEND PROPERTY IMPORTED_CONFIGURATIONS RELEASE)
set_target_properties(Qt5Core PROPERTIES
    IMPORTED_LINK_INTERFACE_LIBRARIES_RELEASE ""
    IMPORTED_LOCATION_RELEASE 
                            "${_qt5_install_prefix}/lib/libQtCore.so.5.0.0"
    IMPORTED_SONAME_RELEASE "libQtCore.so.5"
)


That is, I generate the full file name for the IMPORTED_LOCATION including 
the library prefix and suffix, which are also used for the IMPORTED_SONAME. 
QMake does not provide the library prefix and suffix used in variables, as 
cmake does, but I believe there is also no way to change them in qmake. As a 
result I hardcode the prefixes and suffixes for windows/linux/max - .dll, 
.so etc. 

The Qt QMake maintainer does not like this, and requests that CMake 
determines the prefix and suffix instead. Does CMake provide any way for me 
to get the default prefix and suffix for libraries? If it does then I could 
generate something like this instead:

IMPORTED_SONAME "${CMAKE_LIBRARY_PREFIX}QtCore.${CMAKE_LIBRARY_SUFFIX}.5"

But I still don't think it's necessarily a good idea or the right change to 
make. QMake and CMake don't necessarily agree on what the prefix and suffix 
for libraries will be on different platforms for one thing.

What would you consider a good idea?

Could this have any implications for cross-compiling?

Currently I generate IMPORTED_CONFIGURATIONS for debug and release 
(conditionally, depending on how Qt is built). Should I also generate code 
to set target properties for no configuration? Or should I only do that, and 
not have debug/release versions?:

set_target_properties(Qt5Core PROPERTIES
    IMPORTED_LINK_INTERFACE_LIBRARIES ""
    IMPORTED_LOCATION "${_qt5_install_prefix}/lib/libQtCore.so.5.0.0"
    IMPORTED_SONAME"libQtCore.so.5"
)

Thanks for any guidance,

Steve.