[bug] transient linkage with pure cmake_find_package

As seen in this slack: https://cpplang.slack.com/archives/C41CWV9HA/p1631005375278900

According to the docs it is recommended to ... not need to specify or include anything related with Conan at all; just rely on the find_package feature .... This seems to be not true, as it seems that conan_basic_setup() is still somehow required to get 100% of conans functionality, especially if multiple, chained shared libraries are involved (I guess the LD_LIBRARY_PATH is missing).

Environment Details (include every applicable attribute)

• Operating System+version: Ubuntu 18.04
• Compiler+version: gcc7
• Conan version: 1.40+
• Python version: 3.6.9

Steps to reproduce (Include if Applicable)

clone https://github.com/blackliner/conan_transient_linkage run build.sh

@ericLemanissier 's PR fixes it, while loosing CMake purity: https://github.com/blackliner/conan_transient_linkage/pull/1

Logs (Executed commands with output) (Include/Attach if Applicable)

...
[ 75%] Building CXX object tests/CMakeFiles/lib_a_test.dir/lib_a_test.cpp.o
[100%] Linking CXX executable lib_a_test
/usr/bin/ld: warning: liblib_c.so, needed by //home/fberchtold/.conan/data/lib_b/1.0.0/_/_/package/436fa0a6d3ec3ce29639456d6db8d06cd9bf62c9/lib/liblib_b.so, not found (try using -rpath or -rpath-link)
//home/fberchtold/.conan/data/lib_b/1.0.0/_/_/package/436fa0a6d3ec3ce29639456d6db8d06cd9bf62c9/lib/liblib_b.so: undefined reference to `lum::lib_c::SayHello[abi:cxx11]()'
collect2: error: ld returned 1 exit status
tests/CMakeFiles/lib_a_test.dir/build.make:98: recipe for target 'tests/lib_a_test' failed
make[2]: *** [tests/lib_a_test] Error 1
CMakeFiles/Makefile2:881: recipe for target 'tests/CMakeFiles/lib_a_test.dir/all' failed
make[1]: *** [tests/CMakeFiles/lib_a_test.dir/all] Error 2
Makefile:145: recipe for target 'all' failed
make: *** [all] Error 2
lib_a/1.0.0: 
lib_a/1.0.0: ERROR: Package '4c3f20be28cf1be70e428d9fc0e689236ff00f59' build failed
lib_a/1.0.0: WARN: Build folder /home/fberchtold/.conan/data/lib_a/1.0.0/_/_/build/4c3f20be28cf1be70e428d9fc0e689236ff00f59
ERROR: lib_a/1.0.0: Error in build() method, line 52
        cmake.build()
        ConanException: Error 2 while executing cmake --build '/home/fberchtold/.conan/data/lib_a/1.0.0/_/_/build/4c3f20be28cf1be70e428d9fc0e689236ff00f59' '--' '-j24'

[blackliner]

Nice, thanks, I think thats it for today 😃

[memsharded]

See the error log in the OP, shared objects of transient deps cannot be found during linking.

There are linkers that will skip a library if it doesn’t match its expected architecture, looking like it didn’t found a library that is there, you can find in the filesystem, but it keeps telling you library not found. I have verified this a couple of times, cannot be sure if it is the current issue, but worth at least considering.