Installing a CMake library: also ship find modules for the dependencies?

Question

My CMake library, MyLibrary, has a dependency for OtherLibrary, that I import with a non-standard FindOtherLibrary.cmake.

My library depends on OtherLibrary publicly:

target_link_libraries(MyLibrary PUBLIC OtherLibrary::OtherLibrary)

When I install MyLibrary (together with MyLibraryConfig.cmake), and users want to link against it, they therefore need to import OtherLibrary.

Is there a good practice regarding how to distribute FindOtherLibrary.cmake along MyLibrary?

---

Ideally, one could make things even easier for users of MyLibrary by importing OtherLibrary automatically from the installed config file MyLibraryConfig.cmake, if it contains something like

include(CMakeFindDependencyMacro)
find_dependency(OtherLibrary)

and knows where FindOtherLibrary.cmake is.

Is this at all possible?

Answer 1

I ended up finding a solution to my question.

In principle, it does what @utopia suggested, but in an automated fashion: the end user of my library does not need to set up (or even know about) FindOtherLibrary.cmake. It will be imported automatically by MyLibraryConfig.cmake.

To do so, I install FindOtherLibrary.cmake along MyLibraryConfig.cmake:

install(FILES
          /path/to/MyLibraryConfig.cmake
        DESTINATION
          lib/cmake/MyLibrary
        )
install(FILES
          /path/to/FindOtherLibrary.cmake
        DESTINATION
          lib/cmake/MyLibrary/Modules
        )

And in MyLibraryConfig.cmake I set up how to import it:

include(CMakeFindDependencyMacro)
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_CURRENT_LIST_DIR}/Modules/")
find_dependency(OtherLibrary REQUIRED)

Note that I set the variable CMAKE_MODULE_PATH because it is not possible to specify the location of find modules in find_package or find_dependency (works only for config mode).

Answer 2

"Transitive" behavior for module-mode find_package() is not supported.

In fact, I don't believe it is even possible since it requires modifying downstream CMake module path with information you would not have available to you. That's one of the reasons there is a config-mode find_package() (see here).

To be clear, a user of your library, which has a dependency on a FindModule library, has no choice but to know how to get a copy of the FindModule script and add it to their CMake module path. This is typically done through documentation. You as the author of a library that uses the FindModule cannot shortcut that process for the end user in any general way. So, there is no "good practice" for such a process.

Otherwise, good practice is to use FindModules only for non-CMake projects and use Config.cmake for CMake projects. If a dependent CMake library has no Config.cmake, you're out of luck (tell them they need it to support CMake in a Bug/Issue report).