How do I Install bundled interface dependencies with modern CMake? - c++

Question

What is the proper way to install bundled interface dependencies in Modern CMake?
I have a library MyLib that has an interface dependency on libDep (MyLib.hpp contains #include <libDep.h>). Anything that depends on MyLib also transitively depends on libDep.
libDep is a single header taken from a gist so I have included it part of the source-tree of MyLib
$ tree
.
├── CMake
│   ├── MyLibConfig.cmake.in
│   └── modules
│   └── FindlibDep.cmake
├── CMakeLists.txt
├── include
│   └── MyLib
│   └── MyLib.hpp
├── src
│   └── MyLib.cpp
└── third_party
└── libDep
└── libDep.h
I would like to install libDep with myLib, in with a path like include/MyLib/third_party/libDep.
Here is the CMakeLists for MyLib
cmake_minimum_required(VERSION 3.3.0)
Project(MyLib
DESCRIPTION "Library with bundled interface dependency"
LANGUAGES CXX)
include(GNUInstallDirs)
include(CMakePackageConfigHelpers)
set(CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMake/modules)
# Find LibDep dependency
find_package(libDep REQUIRED)
# MyLib library
add_library(MyLib STATIC
${CMAKE_SOURCE_DIR}/src/MyLib.cpp)
target_include_directories(MyLib
PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include/MyLib>
PUBLIC $<INSTALL_INTERFACE:include/MyLib>)
target_link_libraries(MyLib
INTERFACE libDep)
MyLib locates libDep with FindlibDep.cmake located in CMAKE_MODULE_PATH
find_path(LibDep_INCLUDE_DIR
NAMES LibDep.hpp
PATHS third_party/libDep)
PATH_SUFFIXES Mylib/third_party/libDep)
mark_as_advanced(LibDep_FOUND LibDep_INCLUDE_DIR)
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(LibDep
REQUIRED_VARS
LibDep_INCLUDE_DIR
)
if(LibDep_FOUND)
set(LibDep_INCLUDE_DIRS ${LibDep_INCLUDE_DIR})
endif()
if(LibDep_FOUND AND NOT TARGET MyLib::LibDep)
add_library(MyLib::LibDep INTERFACE IMPORTED)
set_target_properties(MyLib::LibDep PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES ${LibDep_INCLUDE_DIR})
endif()
I install MyLib like
install(TARGETS MyLib
EXPORT MyLibTargets
LIBRARY DESTINATION lib
ARCHIVE DESTINATION lib
RUNTIME DESTINATION bin
INCLUDES DESTINATION include)
include(CMakePackageConfigHelpers)
write_basic_package_version_file(MyLibConfigVersion.cmake)
install(EXPORT MyLibTargets
FILE MyLibTargets.cmake
NAMESPACE MyLib::
DESTINATION lib/cmake/MyLib)
configure_file(CMake/MyLibConfig.cmake.in MyLibConfig.cmake #ONLY)
install(FILES
"${CMAKE_CURRENT_BINARY_DIR}/MyLibConfig.cmake"
"${CMAKE_CURRENT_BINARY_DIR}/MyLibConfigVersion.cmake"
DESTINATION lib/cmake/MyLib)
install(DIRECTORY ${MyLib_PUBLIC_INCLUDE_DIR}
DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
# Package with CPack
include(InstallRequiredSystemLibraries)
include(CPack)
MyLibConfig.cmake.in declares a dependency on libDep
include(CMakeFindDependencyMacro)
# Dependencies
add_library(libDep REQUIRED)
# Add the targets file
include("${CMAKE_CURRENT_LIST_DIR}/MyLibTargets.cmake")
libDep is installed into MyLib's tree with
install(DIRECTORY ${libDep_INCLUDE_DIRS}
DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/MyLib/third_party)
and I copy the find module with
install(FILES
${CMAKE_MODULE_PATH}/FindlibDep.cmake
DESTINATION lib/cmake/MyLib)
Unfortunately users of MyLib don't see FindlibDep.cmake by default
$ cmake ..
CMake Error at /usr/share/cmake-3.10/Modules/CMakeFindDependencyMacro.cmake:48 (find_package):
By not providing "FindlibDep.cmake" in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by "libDep", but
CMake did not find one.
Could not find a package configuration file provided by "libDep" with any
of the following names:
libDepConfig.cmake
libDep-config.cmake
Add the installation prefix of "libDep" to CMAKE_PREFIX_PATH or set
"libDep_DIR" to a directory containing one of the above files. If "libDep"
provides a separate development package or SDK, be sure it has been
installed.
Call Stack (most recent call first):
/usr/local/lib/cmake/MyLib/MyLibConfig.cmake:5 (find_dependency)
CMakeLists.txt:9 (find_package)
-- Configuring incomplete, errors occurred!
The user can manually locate FindlibDep.cmake and add it to their CMAKE_MODULE_PATH but that shouldn't be required.
A reproduction of this issue is available on GitHub.

Answer 1

You need to use the PROJECT_ variable for the source dir instead of the CMAKE_ variable:
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PROJECT_SOURCE_DIR}/CMake/modules)
PROJECT_SOURCE_DIR gets the source dir from the most recently executed project() directive (in this case, your library).
You should also be adding your current CMAKE_MODULE_PATH to the new path, as shown above.