Use colcon plugins

[stelzo]

This PR removes the CMake pipeline and uses ROS Rust colcon and ament plugins instead (#8 and #4).

Release builds work with colcon build --cargo-args --release and cleaning a package before building with colcon build --clean-build.
I am currently missing a simple solution for "installing" launch files. In CMake this could be done with

install(DIRECTORY launch
  DESTINATION share/${PROJECT_NAME}
)

but I haven't found an easy way with cargo yet. How would you rate the relevance for this @m-dahl ?

[m-dahl]

I think keeping the old behaviour has some benefits (no additional dependencies, easy to install stuff as you mentioned). What to you think about something like this to show both approaches?

[stelzo]

I think it is a good approach in theory but in practice it makes the repo a little bit more overhead when using it as a template. I wanted to look into an "ROS installation step" via build.rs but didn't do it yet. I am also waiting for colcon/colcon-cargo#22 so the plugins can be downloaded with pip rosdep.
It would reduce the overhead for adding Rust nodes in general and make the process more seamless. With installation and rosdep solved, I would prefer using only the colcon plugins and remove cmake completely. I would argue that dependencies installed via rosdep are ROS-toolchain-native and thus okay for the process.

[m-dahl]

Hi. Just to let you know I will get back to this shortly, sorry I haven't worked on open source stuff for a while.

[stelzo]

No problem, there was some progress to simplify the steps to install colcon tools in the meantime. Also, installing folders is possible inside Cargo.toml, so there is no need for a build.rs script.

[package.metadata.ros]
install_to_share = ["launch"]

Here are some relevant links if you or anyone is interested.
colcon/colcon-cargo#22
colcon/colcon-ros-cargo#26
ros2-rust/cargo-ament-build#12

This will reduce the overhead of installing the additional Rust tooling to a single pip install colcon-ros-cargo or make it a rosdep dependency. The biggest missing part is cargo-ament-build, which is ongoing right now. I will update the PR afterwards.