[CMake] transitive linking with separate projects

[Alexander Dahl]

Hei hei, 

we faced a build problem with transitive linking of separate projects
where I can't find the right solution on my own. I hope someone can give
me a hint. I prepared a test case with two libraries libfoo and libbar
and an application baz. libfoo is on his own, libbar calls a function
from libfoo and baz calls the function from libbar calling libfoo. So
the dependencies are like this:

baz -> libbar -> libfoo

baz doesn't need to know of libfoo because it just calls libbar, so I
thought.

Now the projects are separated and both libraries come with cmake
package configuration files. For linking libfoo in libbar I do the
following:

find_package(FOO)
target_link_libraries(BAR_SRC foo-shared)

foo-shared is the target libfoo exports via cmake package
configuration. This works and ldd shows libbar is correctly linked
against libfoo.

Now when compiling baz I more or less do the same:

find_package(BAR)
target_link_libraries(BAZ_SRC bar-shared)

However building baz fails with the following error:

% make
[100%] Building C object src/CMakeFiles/baz.dir/baz.c.o
Linking C executable baz
/usr/bin/ld: cannot find -lfoo-shared
collect2: ld returned 1 exit status
make[2]: *** [src/baz] Fehler 1
make[1]: *** [src/CMakeFiles/baz.dir/all] Fehler 2
make: *** [all] Fehler 2

It seems like cmake tries to link against libfoo here but does not know
anything about it. If I add find_package(FOO) to baz obviously the
target is imported from libfoo cmake package files. The question is, if
I know nothing about the requirements of libbar and want to avoid adding
find_package statements for those requirements to baz, how would I do
this?

I put all the code on GitHub, so if someone maybe could have a look?

https://github.com/LeSpocky/libfoo
https://github.com/LeSpocky/libbar
https://github.com/LeSpocky/baz

Greets
Alex

-- 
»With the first link, the chain is forged. The first speech censured,
the first thought forbidden, the first freedom denied, chains us all
irrevocably.« (Jean-Luc Picard, quoting Judge Aaron Satie)
*** GnuPG-FP: 02C8 A590 7FE5 CA5F 3601  D1D5 8FBA 7744 CC87 10D0 ***