[ros-users] cmake link_directories warnings for Maverick

[Jack O'Quin]

On Wed, Jan 5, 2011 at 8:30 PM, Brian Gerkey <gerkey at willowgarage.com> wrote:
> On Wed, Jan 5, 2011 at 5:14 PM, Jack O'Quin <jack.oquin at gmail.com> wrote:
>> I noticed in some build output lately that under Maverick cmake prints
>> warnings like this:
>>
>> CMake Warning (dev) at src/node/CMakeLists.txt:2 (link_directories):
>>  This command specifies the relative path
>>
>>    art_map/lib
>>
>>  as a link directory.
>>
>>  Policy CMP0015 is not set: link_directories() treats paths relative to the
>>  source dir.  Run "cmake --help-policy CMP0015" for policy details.  Use the
>>  cmake_policy command to set the policy and suppress this warning.
>> This warning is for project developers.  Use -Wno-dev to suppress it.
>>
>> I am still running Lucid and Karmic, and I do not see those warnings
>> during development. The build still seems to work, AFAICT.
>>
>> I do use link_directories() in some places, based on these ROS build
>> recommendations:
>>
>>  http://www.ros.org/wiki/rosbuild/CMakeLists/Examples#Adding_compile_.2BAC8_link_flags
>
> The example in that section that uses `link_directories()` is linking
> against a library that's external to ROS.  The warning you're getting
> suggests that you're adding part of your package's directory tree to
> the linker search path.  That's not necessary if you're linking
> against a library that you're also building in that package with
> CMake.  Are the libraries in `art_map/lib` built by something else?

No, they are built by cmake in the same package.

I feel sure the link_directories was needed at some point, perhaps for
boxturtle. If this is no longer needed in cturtle or unstable, I'll
remove it.

>> Are those recommendations obsolete?
>>
>> Some on-line sources suggest that link_directories() should no longer be used:
>>
>>  "Don't use LINK_DIRECTORIES. Consider it deprecated. Specify the
>> full path to the library instead in the TARGET_LINK_LIBRARIES call."
>>
>> Should we start setting absolute path names on target_link_libraries() instead?
>
> Troy just told me about this the other day.  I guess that CMake now
> wants full paths to all libraries, instead of using search paths and
> short names.  I'm not sure that I agree with the motivation for it,
> but perhaps it's the right way to go.  I think that we should hold off
> on changing our code until rosbuild2 comes into use with eturtle,
> because it'll involve changes in how we use CMake.

Sounds reasonable, I'll stay tuned.
-- 
 joq