Understanding the Build-system

The build system is described by the CMakeLists.txt and is composed of few projects each responsible for a specific task. Once configured, the Outer Project is responsible for driving the overall build composed of multiple project called external project. Here is the list of external project:

• CMakeProject-src-download

• CMakeProject-binary-download

• CMakeProject-build

• CMakePythonDistributions: This corresponds to the Inner Project represented below.

The flow chart represented below illustrates which external projects are included based on the configure options and describes the role of each one:

        flowchart LR
    subgraph OP[Outer Project]
        style OP fill:#FFF0D7
        configure["CMakeLists.tct"]
        ask_download{"Download source?"}
        download_source["Download Source archive"]
        reuse_source_dir["Re-use source directory"]
        ask_build{"Build from Source?"}
        download_binaries["CMakeProject-binary-download"]
        build_cmake["CMakeProject-build"]
        strip_executables["Strip executables"]
        ask_inner_build{"Which files to install?"}
        install_pre_built["Install prebuilt binaries"]
        install_cmake_project["Install CMake project"]

        configure --> ask_download

        subgraph EP1[ExternalProject: CMakeProject-src-download]
            style EP1 fill:#E7CA92
            ask_download -->|yes| download_source
            ask_download -->|no| reuse_source_dir
        end

        download_source --> ask_build
        reuse_source_dir --> ask_build

        subgraph EP2[External Projects]
            style EP2 fill:#E7CA92
            ask_build -->|no| download_binaries
            ask_build -->|yes| build_cmake
            build_cmake --> strip_executables
        end

        download_binaries --> ask_inner_build
        strip_executables --> ask_inner_build

        subgraph IP[Inner Project: CMakePythonDistributions]
            style IP fill:#a1acc2
            ask_inner_build -->|no| install_pre_built
            ask_inner_build -->|yes| install_cmake_project
        end
    end
    

Node Title	Description
CMakeLists	CMake configuration file
Download source ?	If option CMakeProject_SOURCE_DIR is set, skip source download.
Download Source archive	External project downloading archives from https://cmake.org/files/.
Re-use source directory	Empty external project.
Build from Source ?	Answer based on option BUILD_CMAKE_FROM_SOURCE
CMakeProject-binary-download	External project downloading pre-built binary archives from https://cmake.org/files/.
CMakeProject-build	External project building CMake from source.
Strip executables	If possible, reduce wheel size stripping cmake, cpack and ctest executables
Which files to install?	Answer based on option BUILD_CMAKE_FROM_SOURCE
Install prebuilt binaries	Recursively glob all files and explicitly add install rules.
Install CMake project	Achieved by including ${CMakeProject_BINARY_DIR}/cmake_install.cmake