[CMake] CMake Digest, Vol 134, Issue 1

[Knox, Kent]

Hi Daniel~

" Suppose you have libA that optionally uses zip functionality (say by some option USE_ZLIB in libA's CMakeLists.txt). This means libA will optionally have -lz in its INTERFACE_LINK_LIBRARIES (exported into liba-config.cmake)."

I think the best way to handle this is to turn 'transitive library linking' off.  It seems to me that the use of zip functionality is an implementation detail of libA, that no clients should be aware of.  I do this in my projects with a special form of the target_link_libraries( ) command:
`target_link_libraries( libA PRIVATE ${ZLIB_LIBRARIES} )`

I believe PRIVATE, PUBLIC, INTERFACE keywards were added in cmake 2.8.12

Kent
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Message: 4
Date: Mon, 01 Jun 2015 11:03:53 +0200
From: Daniel Wirtz <daniel.wirtz at simtech.uni-stuttgart.de>
To: cmake at cmake.org
Subject: [CMake] Conditional transitive link libraries
Message-ID: <556C1FF9.6040609 at simtech.uni-stuttgart.de>
Content-Type: text/plain; charset=utf-8; format=flowed

Hello all,

I'm struggling with the CMake "Config"-based package description when using two depending packages where the upstream package has optional link libraries.

Suppose you have libA that optionally uses zip functionality (say by some option USE_ZLIB in libA's CMakeLists.txt). This means libA will optionally have -lz in its INTERFACE_LINK_LIBRARIES (exported into liba-config.cmake).
Now, if you have a libB using libA via find_package(libA), how do you know if libA has been built with or without zlib support when both libraries are installed and exported with CMake's package config system?

I know that the link library information is treated transitively and will be propagated to the link libraries of libB, hence -lz will appear whenever linking against libB. However, the PATH to libz is nowhere included; consequently, the link fails with "could not find library z" 
unless you magically knew that libz is a dependent link library of libA and where to include it from. Including the absolute path to libz in libA's config is also not the way to go, as it ruins the portability over different systems.

Is there a "native" CMake way?

Thanks!

--
Dr. Daniel Wirtz
Dipl. Math. Dipl. Inf.
SRC SimTech
Pfaffenwaldring 5a
+49 711 685 60044