Gaudi CMake Documentation ========================= This documentation is the updated version of https://twiki.cern.ch/twiki/bin/view/LHCb/GaudiCMakeConfiguration and is based on `CMake 3.15 `__. It was written after the modernization of the configuration of Gaudi. Introduction ------------ `CMake `__ is an Open Source, cross-platform configuration and build tool used in several projects around the world. Among its advantages we can count the support that comes from a large user base and the CMake configuration language that doubles as a portable and powerful scripting language. The main drawbacks of CMake are the syntax of its language (not very nice looking) and the lack of support for runtime environment definition, but, thanks to the power of the language, we can overcome the drawbacks. Here I'll describe how to write the CMake configuration for projects and packages. See also the `CMake Documentation `__. Understanding and Writing CMake Code ------------------------------------ A minimal introduction on the CMake syntax and conventions is mandatory for people who never used it. info The syntax highlighting in the code blocks is not correct because TWiki.SyntaxHighlightingPlugin does not understand the CMake language. In CMake every statement is a function call, written as an identifier followed by optional spaces and the arguments to the function as a space-separated list enclosed in parentheses. The arguments to a function can span over several lines, and double quotes (``"``) can be used to pass arguments containing spaces and new-lines. Examples of functions: .. code-block:: cmake message("hello world") .. code-block:: cmake if(1 GREATER 0) message("this is true") else() message("this is false") endif() One can add comments to the code using ``#`` at the beginning of the comment text (spaces preceding ``#`` are ignored), like, e.g., in Unix shells and Python: .. code-block:: cmake # I'm a comment if(TRUE) # this is always printed message("it's true") else() # this is never printed message("it's false") endif() The CMake language supports variables, which are set with the function ``set`` and dereferenced with ``${...}``, e.g.: .. code-block:: cmake set(MyMessage "hello world") message(${MyMessage}) Dereferencing of variables can be nested and works also in between double quotes: .. code-block:: cmake set(name MyName) set(${name}_msg "This is${name}") message(${${name}_msg}) There is something special in the way CMake functions are invoked. CMake functions and macros (similar to functions) accept variable number of arguments and the only separators between arguments are spaces (tabs and new-lines too), so it might not be obvious how to pass optional arguments (like it's done in Python with named arguments). The solution found by CMake developers is to use *keyword-separated* lists of arguments. For example, we can imagine a function that requires a mandatory argument *name* and two optional lists of files, C sources and C++ sources. In CMake you could find it invoked like this: .. code-block:: cmake make_a_library(MyLibrary C_SOURCES file1.c file2.c file3.c) make_a_library(MyLibrary CXX_SOURCES file1.cpp file2.cpp file3.cpp) make_a_library(MyLibrary C_SOURCES file1.c file2.c file3.c CXX_SOURCES file1.cpp file2.cpp file3.cpp) Warning: Function names are case-insensitive, but variable names are case sensitive as well as string comparison. CMake Configuration of a Gaudi-based Project -------------------------------------------- Several steps must be performed to build a Gaudi based project: - Set up the build environment (if not already set up) - Configure the project with CMake (generate *Makefile* or *build.ninja*) - Compile the source files and link the binaries - Test the previously build binaries (optional but recommended) Set up the build environment ---------------------------- To set up the build environment, some environment variables need to be set. * **BINARY_TAG**: the variable that describe the platform * **CMAKE_PREFIX_PATH**: is a path-like variable that must contain the list the list of path to: * the compiler e.g. *g++*, *clang++* (the compiler may be a wrapper) * the build system e.g. *make*, *ninja* * all third-party dependencies e.g. Boost, ROOT * **PATH** (optional): may contain the paths to the compiler and the build system There are several ways to set these variables: * use *export* several time (or run a shell script that will do so) * source a view (a shell script that sets the aforementioned variables to a directory of symlinks) * specify a toolchain to the configuration With *export* ~~~~~~~~~~~~~ .. code-block:: bash export BINARY_TAG="x86_64-centos7-gcc8-opt" export CMAKE_PREFIX_PATH="/path/to/g++:/path/to/boost:/path/to/ROOT:..." It is also possible to list the call to *export* in a shell script to be able to source it later on. With a view ~~~~~~~~~~~ .. code-block:: bash source/cvmfs/sft.cern.ch/lcg/views/LCG_96/x86_64-centos7-gcc8-opt/setup.sh # the views may lack some stuff export CMAKE_PREFIX_PATH="$CMAKE_PREFIX_PATH:/cvmfs/sft.cern.ch/lcg/releases/LCG_95/vectorclass/1.30/x86_64-centos7-gcc8-opt:/cvmfs/projects.cern.ch/intelsw/psxe/linux/x86_64/2019/vtune_amplifier" Warning: Sourcing a view is not the same as sourcing a shell script that uses *export*. A view is a directory of symbolic links and a *setup.sh* script. With a toolchain ~~~~~~~~~~~~~~~~ .. code-block:: bash # Either use -D CMAKE_TOOLCHAIN_FILE=/path/to/a/toolchain # at configure time when calling cmake # or ln -s /path/to/a/toolchain toolchain.cmake # right away Configuration of the project ---------------------------- The configuration requires at least CMake 3.15. CMake 3.15.0 was released on 2019-07-17. .. code-block:: bash # Check CMake version cmake --version # if version < 3.15 export PATH="/cvmfs/lhcb.cern.ch/lib/contrib/CMake/3.15.2/Linux-x86_64/bin:$PATH" The configuration is the step when CMake is called and produces the files for the build system (e.g. *make*, *ninja*). Two directories must be specified: * the source tree: contains the sources * the build tree: will contain the outputs of the build .. code-block:: bash cmake -S . -B build.$BINARY_TAG # options can be passed at configure time cmake -S . -B build.$BINARY_TAG -G Ninja # set the build system cmake -S . -B build.$BINARY_TAG -D GAUDI_USE_AIDA=OFF # enable/disable a third party dependency cmake -S . -B build.$BINARY_TAG -D CMAKE_BUILD_TYPE=Developer # select a build type (a set of compile and link options) cmake -S . -B build.$BINARY_TAG -DCMAKE_TOOLCHAIN_FILE=toolchain.cmake # specify a toolchain # several options may be specified with: -D ... -D ... -D ... # ccmake and cmake-gui can be used cmake -LH build.$BINARY_TAG # to see all the options and their help messages Compilation of the project -------------------------- Once the project is configured, several files are already in the build tree. They will be used to compile the project. .. code-block:: bash cd build.$BINARY_TAG make # or ninja or an IDE # or directly with CMake cmake --build build.$BINARY_TAG Test the binaries ----------------- Good developers test their code. To run the tests: .. code-block:: bash cd build.$BINARY_TAG ctest -j --output-on-failure --schedule-random The wrapper ----------- Doing all these steps each time may be tedious so there is a *Makefile* file at the top level of Gaudi-based projects to wrap the call to these commands. .. code-block:: bash # configure + compile make # run the tests make test The wrapper uses a toolchain if a file called *toolchain.cmake* exists in the current directory. It might be useful to have a shell function to easily switch from one toolchain to another. .. code-block:: bash function switch_platform { export BINARY_TAG=$1 rm -f toolchain.cmake ln -s /cvmfs/.../toolchains/$1.cmake toolchain.cmake # !! Use the right path on CVMFS } Use the software ---------------- In order to use the previously built software, it is mandatory to use the **runtime environment** (it may differ from the build environment). The runtime environment is generated by the configuration at configure time in the build tree in a script called *run*. .. code-block:: bash cd build.$BINARY_TAG # ./run ./run listcomponents -h ./run gaudirun.py Modify the configuration ------------------------ At the top level directory of a project and in every sub-project (package) there must be one file: ``CMakeLists.txt`` The file at the top level directory describes the build of the whole project: * may contain a licence block * contains documentation (how to configure it, available options) * describes the project (name, version) * fetches the dependencies * sets options for the build (C++ standard) * list all the sub-projects (packages in sub-directories) * handles the installation The files in the sub-projects directories: * describes the binaries that will be compiled (libraries, modules, executable, ROOT dictionaries) * register tests for these binaries * handles the installation of their python packages and scripts Configuration of sub-projects ----------------------------- Look and feel of typical sub-project ``CMakeLists.txt``: .. code-block:: cmake # {licence block if needed} # {SubdirName} subdirectory # Build the library gaudi_add_library(SubdirNameLib SOURCES src/Lib/Counter.cpp src/Lib/Event.cpp LINK PUBLIC GaudiKernel) # Build the plugin gaudi_add_module(SubdirName SOURCES src/AbortEvent/AbortEventAlg.cpp src/AlgSequencer/HelloWorld.cpp LINK GaudiKernel GaudiExamplesLib ROOT::Tree Rangev3::rangev3) if(GAUDI_USE_AIDA) # optional dependency target_sources(SubdirName PRIVATE src/EvtColsEx/EvtColAlg.cpp src/Histograms/Aida2Root.cpp) target_link_libraries(SubdirName PRIVATE AIDA::aida) endif() # Build the executable gaudi_add_executable(Allocator SOURCES src/Allocator/Allocator.cpp src/Allocator/MyClass1.cpp LINK SubdirNameLib GaudiKernel) # Generate GaudiExamples_user.confdb gaudi_generate_confuserdb() # Tests gaudi_add_tests(QMTest) gaudi_add_pytest(tests/pytest) # Compiled python module gaudi_add_python_module(PyExample SOURCES src/PythonModule/Functions.cpp src/PythonModule/PyExample.cpp LINK Python::Python Boost::python) # ROOT dictionaries gaudi_add_dictionary(SubdirNameDict HEADERFILES src/IO/dict.h SELECTION src/IO/dict.xml LINK SubdirNameLib) # Install python modules gaudi_install(PYTHON) # Install other scripts gaudi_install(SCRIPTS) Why is the explicit list of sources mandatory? Even tough CMake is able to use glob patterns with ``file(GLOB...)``, those glob patterns are expanded at configure time and their results hardcoded in ``makefile`` or ``build.ninja`` or whichever file used by IDEs. This means that if a new file that matches the pattern is added, there is no way for the build system (make, ninja...) to notice it. The first solution is to reconfigure the project each time a new file is added to update the hardcoded list of sources. (This can be done either by rerunning the configuration command or by touching a ``CMakeLists.txt``.) The other solution would be to forward the glob pattern to the build system. CMake offers a way to do so: ``file(GLOB ... CONFIGURE_DEPENDS)`` but for the time being, only Makefiles generators and Ninja are supported, meaning that people using IDEs would still have to reconfigure the project themselves. Adding a new sub-project to the project --------------------------------------- If a new sub-project is added to a project, its directory must be added to the list of sub-projects in the top-level ``CMakeLists.txt`` alongside with the other sub-projects with: .. code-block:: cmake add_subdirectory(SubdirName) The directory of the sub-project must also contain a ``CMakeLists.txt`` that looks like the one above. Adding a new third-party dependency ----------------------------------- First, look in the documentation of the dependency. If it uses CMake, it may provide a **config file** (a file named ``{DependencyName}Config.cmake``). Otherwise, it is necessary to write a **find module file** (a file named ``Find{DependencyName}.cmake``) that will do the look up of this dependency (find the include directory, find all the libraries, find any other useful files provided by the dependency and create some IMPORTED targets). (Have a look at the other find module files in the project to get an idea of what it should look like. They should be in ``cmake/modules``.) Then, add the look up of the dependency in the file ``cmake/{ProjectName}Dependencies.cmake`` (replace with the name of the dependency and with the minimal required version). .. code-block:: cmake # For mandatory dependencies find_package( ${__quiet}) set_package_properties( PROPERTIES TYPE REQUIRED) # For optional dependencies if(GAUDI_USE_) find_package( ${__quiet}) if(CMAKE_FIND_PACKAGE_NAME) # if the lookup is perform from ProjectConfig.cmake # then, all optional dependencies become required set_package_properties( PROPERTIES TYPE REQUIRED) else() set_package_properties( PROPERTIES TYPE RECOMMENDED) endif() endif() # and add the option GAUDI_USE_ in the top level CMakeLists.txt #Finally, it is usable. gaudi_add_(... LINK ... Dependency::Target ...) Removing an old third-party dependency -------------------------------------- If a dependency is no longer used (nothing defined by it is used anywhere), it is no use keeping to look for it. In this case, remove the chunk of code that looks for it in ``cmake/{ProjectName}Dependencies.cmake`` (see Adding a new third-party dependency). Then remove the **find module file** ``Find{DependencyName}.cmake`` in cmake/modules if it exists. Gaudi CMake functions to help the configuration ----------------------------------------------- All the ``gaudi_*()`` functions are defined by Gaudi. Their content and documentation can be found `here `__ in ``GaudiToolbox.cmake``. List of defined functions: * ``gaudi_add_library()`` * ``gaudi_add_header_only_library()`` * ``gaudi_add_module()`` * ``gaudi_add_python_module()`` * ``gaudi_add_executable()`` * ``gaudi_add_tests()`` * ``gaudi_add_dictionary()`` * ``gaudi_install()`` * ``gaudi_generate_confuserdb()`` * ``gaudi_check_python_module()`` * ``gaudi_generate_version_header_file()`` Building a stack of project at once ----------------------------------- With the configuration it is possible to build a stack of project at once. CMake may configure all the projects of the stack in one go, enabling the compilation to be done in parallel for all the projects. Example of a stack: Gaudi, LHCb, Lbcom, Rec, Brunel .. code-block:: bash mkdir workspace cd workspace git clone project_url # of all the projects of the desired stack cat < CMakeLists.txt cmake_minimum_required(VERSION 3.15) project(LHCbFullStack LANGUAGES CXX DESCRIPTION "LHCb full stack") enable_testing() add_subdirectory(Gaudi) add_subdirectory(LHCb) # add_subdirectory() ... all the other projects of the stack EOF Using GaudiObjDesc (LHCb-specific) ---------------------------------- Warning: GaudiObjDesc has not been modernized because it should be removed soon. Do not use GaudiObjDesc in future project. However, if you need to maintain a package that uses GaudiObjDesc have a look at the old documentation `here `__ Pro tip: do not document too much GaudiObjDesc so that people begrudge to use GaudiObjDesc. Update old Gaudi Projects to the new CMake Configuration in v35 --------------------------------------------------------------- When updating an existing Gaudi Project to use v35, the following changes need to be made: * Add a ``project(PROJECTNAME)`` line in the top level CMakeLists.txt * change ``find_package(GaudiProject)`` to ``find_package(Gaudi)`` in the top level CMakeLists.txt * remove any calls to ``gaudi_project(...)`` * explicitly add all subdirectories that contain a CMakeLists.txt with ``add_subdirectory(...)`` * update any calls to ```gaudi_add_library``` to use the new signature * update any calls to ```gaudi_add_module``` to use the new signature * change ``gaudi_install_*()`` to ``gaudi_install(*)`` * Export all libraries and modules as targets with ``install(TARGETS ... EXPORT ...)`` * add a call to ``gaudi_install(CMAKE)`` int the top level CMakeLists.txt * add a CMake config file ``cmake/PROJECTNAMEConfig.cmake`` which should include the targets file For a concrete example, see the changes needed to update key4hep framework core library: https://github.com/key4hep/k4FWCore/pull/19/files