[ros-users] [Discourse.ros.org] [Next Generation ROS] Creating a top CMakeLists.txt to standardize all the ROS2 core packages building with CMake

[Geoffrey Biggs]

Repositories such as `rcl` are not a single CMake project. They are a collection of related packages and they do not necessarily need or want to be built as a single CMake project. They are designed to be build individually but in the correct order. The build order may be non-trivial, for example, or you might ant to only build one package from a large repository. This is why although you can clone the repository to get all the packages at once, you need to use a tool like `colcon` to build them. `colcon` will sort out things like the build order automatically based on information in the `package.xml` file, which often contains information not found in the `CMakeLists.txt` file. Furthermore, some repositories may have a mix of C/C++ and Python (or other language) packages. It wouldn't be feasible to insist that these all have a top level `CMakeLists.txt` file.





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