symlink-install only creates symlinks in the build folder NOT the install folder, why?

[TheConstructAi]

Hi to reproduce this issue:

mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
git clone https://bitbucket.org/theconstructcore/ros2_build_tests.git
cd ~/ros2_ws
source /opt/ros/galactic/setup.bash
colcon build --symlink-install
source install/setup.bash
ros2 run build_test_pkg script1_exe

Expected behavior

I would expect that the symlinks are inside the install folder which is the one form where we use the files

Actual behavior

It's sourcing the build folder, which I don't understand its use then

this example uses a yaml file from the install path, and no matter what you do, you need to compile to update those changes, because the file used is the one in the install folder.

Is this intended to work like this? what is the advantage then of using symlink apart from the fact of not having to compile when we only change python scripts?

And even this it's not clear how this is accomplished, where are the symlinks in the install folder to be able to use the source version of the python scripts without compiling again?

I think this is a recurring question and it's really confusing for users.

[cottsay]

This behavior is supported by the underlying build system and isn't implemented by colcon directly.

For example, here is where colcon tells ament_cmake packages to symlink install: https://github.com/colcon/colcon-ros/blob/d7a66047e5aac95ee31eee2ef837f76919e2be9e/colcon_ros/task/ament_cmake/build.py#L50-L53

The symlink installation for Python packages is more complex and relies on the develop verb. In truth, the source code for your example build_test_pkg package uses an "egg-link" file to the package subdirectory in build, so changing the sources will affect the installed environment as you desire. Unfortunately, the data_files specified in your setup.py don't get symlinked by Python. The fact that they're using a non-symlink-based system (egg-link) to take care of linking the Python code makes me wonder if the lack of cross-platform symlink support is one reason that it isn't done for data_files.

[Usimian]

Thanks for the explanation.
Is there a fix?

[vanem]

This is confusing and inconsistent: the launch files declared with CMakeLists.txt install directives ARE symlinked in the install share folder!

[HomeworldL]

I've encountered this problem as well. I need to use colcon build to recompile to update my changes (like .launch files). All the links are in the build folder. An inelegant way is to manually copy the links in the build to the install, but that is somewhat bothersome. Is there a better solution now?

[RodBelaFarin]

Any news on this? It is still not working as expected.

[cottsay]

I think this issue is mostly a duplicate of #169. There is discussion there of a possible solution. If you'd like to see that solution merged, please test it and provide feedback.