Let’s assume I have a library that links privately to an imported, header only library:
FindAsio.cmake (unfortunately does not export itself)
add_library(asio::asio INTERFACE IMPORTED)
set_target_properties(asio::asio PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES ${Asio_INCLUDE_DIR}
INTERFACE_COMPILE_DEFINITIONS ASIO_STANDALONE)
and then the project of choice:
add_library (fineftp all_my_sources.cpp)
add_library (fineftp::fineftp ALIAS fineftp)
target_link_libraries(fineftp
PRIVATE
asio::asio
Threads::Threads
)
Exporting this library with CMake leads to the following statements in fineftpTargets.cmake:
add_library(fineftp::server STATIC IMPORTED)
set_target_properties(fineftp::server PROPERTIES
INTERFACE_COMPILE_DEFINITIONS "ASIO_STANDALONE;__USE_FILE_OFFSET64=1"
INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
INTERFACE_LINK_LIBRARIES "\$<LINK_ONLY:asio::asio>;\$<LINK_ONLY:Threads::Threads>"
)
This requires the user to locate asio on their machine, too, though it’s a private requirement of a header only library, e.g. there will be no linkage.
Not locating asio as a consumer of fineftp-server leads to the following CMake Error.
CMake Error at CMakeLists.txt:9 (add_executable):
Target "fineftp_example" links to target "asio::asio" but the target was
not found. Perhaps a find_package() call is missing for an IMPORTED
target, or an ALIAS target is missing?
How can I avoid this usage requirement? Is this a CMake bug? Or is it necessary because asio::asio could have other transitive dependencies which need to be linked?
The following project has this problem, try building / installing it and then building the samples against the installed version: