linker error for bullet soft body

[Karsten1987]

When compiling the gazebo_ros_pkgs on mojave, I run into the following linker errors:

[14%] Linking CXX shared library libgazebo_ros_node.dylib
[ 17%] Linking CXX shared library libgazebo_ros_utils.dylib
ld: library not found for -lBulletSoftBody
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ld: library not found for -lBulletSoftBody
make[2]: *** [libgazebo_ros_node.dylib] Error 1
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[1]: *** [CMakeFiles/gazebo_ros_node.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
make[2]: *** [libgazebo_ros_utils.dylib] Error 1
make[1]: *** [CMakeFiles/gazebo_ros_utils.dir/all] Error 2
make: *** [all] Error 2
--- stderr: gazebo_ros
ld: library not found for -lBulletSoftBody
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ld: library not found for -lBulletSoftBody
make[2]: *** [libgazebo_ros_node.dylib] Error 1
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[1]: *** [CMakeFiles/gazebo_ros_node.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
make[2]: *** [libgazebo_ros_utils.dylib] Error 1
make[1]: *** [CMakeFiles/gazebo_ros_utils.dir/all] Error 2
make: *** [all] Error 2
---
Failed   <<< gazebo_ros	[ Exited with code 2 ]

I am a bit puzzled about it because just before, it correctly finds the bullet dependencies:

-- Checking for module 'bullet>=2.82'
--   Found bullet, version 2.88

And indeed, it seems like bullet is correctly installed:

 ➭ locate libBulletSoftBody
/usr/local/Cellar/bullet/2.88/lib/libBulletSoftBody.2.88.dylib
/usr/local/Cellar/bullet/2.88/lib/libBulletSoftBody.a
/usr/local/Cellar/bullet/2.88/lib/libBulletSoftBody.dylib
/usr/local/lib/libBulletSoftBody.2.88.dylib
/usr/local/lib/libBulletSoftBody.a
/usr/local/lib/libBulletSoftBody.dylib

any idea on what's going wrong here?

[Karsten1987]

while debugging, I added the hardcoded path the bullet and this seemed to work:

link_directories("/usr/local/lib/")

This made me wonder where this dependency comes in in the first place, which I couldn't resolve. I believe there is the dependency of bullet not correctly exported.

[chapulina]

Gazebo should be the one pulling Bullet, here.

[Karsten1987]

So after a bit of digging, I believe I found what's going wrong here.
Gazebo does check for bullet, but does not export the bullet libraries as targets, but rather simply adds a linker flag

add_definitions( -DLIBBULLET_VERSION=${BULLET_VERSION} )

That works as long as the library is being found on a default LD path. On my OSX machine it is unfortunately not the case. That's why I have to manually add the gazebo_LIBRARY_DIRS onto the search path. The PR #963 does exactly that.

I personally think that link_libraries should be avoided as much as possible and would rather hope that the cmake logic of exporting bullet could change at some point in the gazebo cmake files.

[chapulina]

Thanks for the fix. Feel free to open PRs against crystal / dashing if this needs backporting.

would rather hope that the cmake logic of exporting bullet could change at some point in the gazebo cmake files.

You could ticket an issue for Gazebo or, even better, make a PR fixing this upstream 😉