Create CMake/CPack <Library>Config.cmake for shared library - cmake

Question

I have the simplest possible c-library which builds and is packed using the following CMakeLists.txt:
cmake_minimum_required(VERSION 3.5)
project (libfoo C)
add_library(foo SHARED impl.c)
target_link_libraries(foo)
install(TARGETS foo LIBRARY DESTINATION lib/)
install(FILES public_header.h DESTINATION include/libfoo)
set(CPACK_GENERATOR "TGZ")
include(CPack)
Working example is located here: https://github.com/bjarkef/cmake-simple/tree/master/libfoo
I execute mkdir -p build; (cd build/; cmake ../; make all package;) to build a .tar.gz package with the compiled shared library along with its public header file. This is all working fine.
Now I wish to modify the CMakeLists.txt to create the FooConfig.cmake and FooConfigVersion.cmake files needed for CMake find_package in a different project to find the foo library. How do I do this?
I have discovered I should used the CMakePackageConfigHelpers: configure_package_config_file and write_basic_package_version_file, and I should create a FooLibraryConfig.cmake.in file. However I cannot figure out how to put it all together.
Note that it is important the the resulting .cmake files only contains relative paths.

Answer 1

I have cmake module included in the top level CmakeList.txt:
# Generate and install package config files
include(PackageConfigInstall)
Within the generic PackageConfigInstall.cmake file, the config files are created from the cmake.in files, and installed. This module can be reused for other packages.
include(CMakePackageConfigHelpers)
# Generate package config cmake files
set(${PACKAGE_NAME}_LIBRARY_NAME ${CMAKE_SHARED_LIBRARY_PREFIX}${PACKAGE_NAME}${CMAKE_STATIC_LIBRARY_SUFFIX})
configure_package_config_file(${PACKAGE_NAME}-config.cmake.in
${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config.cmake
INSTALL_DESTINATION ${CMAKE_INSTALL_DIR}/${PACKAGE_NAME}
PATH_VARS LIB_INSTALL_DIR INCLUDE_INSTALL_DIR APP_INCLUDE_INSTALL_DIR )
configure_file(${PACKAGE_NAME}-config-version.cmake.in ${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config-version.cmake #ONLY)
# Install package config cmake files
install(
FILES
${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config.cmake
${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config-version.cmake
DESTINATION
${CMAKE_INSTALL_DIR}/${PACKAGE_NAME}
COMPONENT
devel
)
You'll need a package file for your library, such as your_lib-config.cmake.in, which will become your_lib-config.cmake. This will contain the include and library variables that can be used.
get_filename_component(YOUR_LIB_CMAKE_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
# flag required by CMakePackageConfigHelpers
#PACKAGE_INIT#
set_and_check(YOUR_LIB_INCLUDE_DIR #PACKAGE_YOUR_LIB_INCLUDE_INSTALL_DIR#/hal)
set_and_check(YOUR_LIB_LIBRARY #PACKAGE_LIB_INSTALL_DIR#/#CMAKE_STATIC_LIBRARY_PREFIX##PROJECT_NAME_LIB##CMAKE_STATIC_LIBRARY_SUFFIX#)
set_and_check(YOUR_LIB_LIBRARIES #PACKAGE_LIB_INSTALL_DIR#/#CMAKE_STATIC_LIBRARY_PREFIX##PROJECT_NAME_LIB##CMAKE_STATIC_LIBRARY_SUFFIX#)
You'll also want a config-version.cmake.in file like this:
set(PACKAGE_VERSION #PACKAGE_VERSION#)
# Check whether the requested PACKAGE_FIND_VERSION is compatible
if("${PACKAGE_VERSION}" VERSION_LESS "${PACKAGE_FIND_VERSION}")
set(PACKAGE_VERSION_COMPATIBLE FALSE)
else()
set(PACKAGE_VERSION_COMPATIBLE TRUE)
if ("${PACKAGE_VERSION}" VERSION_EQUAL "${PACKAGE_FIND_VERSION}")
set(PACKAGE_VERSION_EXACT TRUE)
endif()
endif()
There's quite a bit to the packaging scripts to get it all to work just right. I went through a lot of trial and error to finally get something that works on different targets (both linux server and embedded target). I might have left something out, so please just comment and I'll update answer.