What is the difference between colcon-cargo and colcon-ros-cargo

[azerupi]

Hi!

I'm trying to get a better understanding of the build process for ros2_rust and from the READMEs form colcon-cargo and colcon-ros-cargo I didn't find an obvious description of the difference between both.

Both tools seem to be a colcon extension to build Cargo based projects. Why are both required and how do they complement each other?

[maspe36]

This difference has to do with how we identify ROS packages with just a Cargo.toml (colcon-cargo) or ROS packages with a Cargo.toml and a package.xml (colcon-ros-cargo).

colcon-ros-cargo can then call cargo ament_build (from cargo-ament-build). This cargo plugin does additional things like patching message crates in your .cargo/config.toml and also registering artifacts in the ament index.

If you're interested in our build process, and want to contribute to making things (hopefully) a bit simpler, check out this proposal I've been working on #471