Installed libraries instead of newly built ones

[jmirabel]

On 18.04, for a package with library and unit tests on this library, the unit test will find first the installed version of the library, rather than the one in the build folder. On 16.04, the behavior was different.

I couldn't find anything relevant with a websearch (my keywords may have been wrong). It may be related to this module. Two questions:

• Anybody knows why ?
• Anybody encountered this issue ?

[jcarpent]

I think we should export the env viriable for the test containing first the compilations paths.

[jmirabel]

I think I understood the change of behavior. It is because on 16.04, CMake used to set rpath to the correct build folder. On 18.04, it sets runpath.
The order into which shared libs are looked for is: rpath, LB_LIBRARY_PATH and runpath.

[jmirabel]

The issue actually comes from the linker, i.e. ld on linux. In the past, runpath did not exist. When it both became available, runpath became the default. Thus the change of behavior.

Add option -Wl,--disable-new-dtags to CMAKE_EXE_LINKER_FLAG to tell ld to set rpath instead of runpath.

[jmirabel]

Last thought on this.

Setting the environment variable from CMake would work when CMake launch the unit tests. It wouldn't work when the unit test are run manually.

[florent-lamiraux]

The order into which shared libs are looked for is: rpath, LB_LIBRARY_PATH and runpath.

Providing

SET_TARGET_PROPERTIES(${NAME} PROPERTIES BUILD_RPATH
  ${PROJECT_BINARY_DIR}/lib)

to my test, I get
/usr/lib/ccache/g++ -pedantic -Wno-long-long -Wall -Wextra -Wcast-align -Wcast-qual -Wformat -Wwrite-strings -Wconversion -rdynamic CMakeFiles/signal-ptr.dir/signal-ptr.cpp.o -o signal-ptr -Wl,-rpath,/home/florent/devel/pyrene/src/dynamic-graph/build-rel/lib ../lib/libdynamic-graph.so ...
So, option -rpath is present, but the test links with the installed version of the library libdynamic-graph.so.
This seems to refute the above assertion.

[florent-lamiraux]

Add option -Wl,--disable-new-dtags to CMAKE_EXE_LINKER_FLAG to tell ld to set rpath instead of runpath.

This works for me. Should I make a pull request in this project ?

[jmirabel]

This flag should be added only when supported by the linker. I don't know how to get this information...