build: There should be a warning when there are missing links in the workspace dependency graph

[jbohren]

Currently, a user could mistakenly try to overlay system package X by putting its source code into his or her workspace, in order to build package Z which depends on it. However, if package Z depends on package Y which also depends on X, and package Y is not in the workspace, it could lead to package Z being built against the system package X instead of the workspace package X.

catkin build could easily check for this by constructing the dependency graph including the workspace and $CMAKE_PREFIX_PATH, and then determining if there are any paths between workspace packages which include system packages. If so, the user should be warned about the problem.

[wjwwood]

If I understand you correctly this is captured here: #30 and in #90.

[jbohren]

If I understand you correctly this is captured here: #30 and in #90.

This doesn't entirely capture it. These (#30 and #90) will make sure packages in this workspace are ordered correctly, but in the case where an interim dependency exists, the build might be broken. This is really apparent when building c++ libraries that are linked together.

[wjwwood]

I see what you mean, Z' links against Y which is linked against X and not X' as it should (where ' denotes the version in the overlaid workspace)? In some cases the change to the LD_LIBRARY_PATH should be sufficient, but it might fail at linkedit if there are new symbols in the headers of X' which the library of X does not have and you're building with an isolated devel or install setup.

[jbohren]

Yeah, it's not handled by LD_LIBRARY_PATH if the absolute path is given by the CMake module, and this is what happens with catkin packages.

[jbohren]

Also note that now that #249 is merged, users are presented with CMake warnings about conflicting paths like the following:

CMake Warning at /home/jbohren/ws/ascent_sim/src/moveit_ros/planning/plan_execution/CMakeLists.txt:3 (add_library):
  Cannot generate a safe runtime search path for target moveit_plan_execution
  because there is a cycle in the constraint graph:

    dir 0 is [/home/jbohren/ws/ascent_sim/devel/lib]
      dir 1 must precede it due to runtime library [liborocos-kdl.so.1.3]
    dir 1 is [/opt/ros/indigo/lib]
      dir 0 must precede it due to runtime library [libmoveit_planning_pipeline.so]

  Some of these libraries may not be found correctly.

[jbohren]

closing in favor of #30