BoostConfig: Many target-dependent generator expressions evaluate to empty or wrong values.

[jjELT]

This is a copy of the Gitlab Kitware Issue 20611, which applies to both FindBoost and BoostConfig

Maybe you want to deal with it differently?!:

Background

I am linking to the shared variant of Boost::log and would like to copy the shared (.dll / .so) and import (.lib, .dll.a / .a) library files to the output folder using target dependent generator expressions in an post-build command like so:

# Add a post-build command to copy all shared and import libraries
add_custom_command(TARGET ${TARGET_NAME} POST_BUILD
	# Command to copy the shared library.
	COMMAND "${CMAKE_COMMAND}" -E copy_if_different "$<TARGET_FILE:${ITERATED_COMPONENT}>" "${LIBRARY_OUTPUT_DIRECTORY}"
	# Command to copy the import library.
	COMMAND "${CMAKE_COMMAND}" -E copy_if_different "$<TARGET_LINKER_FILE:${ITERATED_COMPONENT}>" "${ARCHIVE_OUTPUT_DIRECTORY}" )

Problem

Many of the properties listed in target dependent generator expressions evaluate to empty or wrong (as far as my understanding goes) values. This is the case for both FindBoost and BoostConfig, i.e. no matter if setting Boost_NO_BOOST_CMAKE=ON or Boost_NO_BOOST_CMAKE=OFF.

Here is a list of some of the values the generator expressions evaluate to:

TARGET_NAME_IF_EXISTS: Boost::log
TARGET_FILE: <BOOST_ROOT>/lib/shared/libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_FILE_BASE_NAME: Boost::log
TARGET_FILE_PREFIX: 
TARGET_FILE_SUFFIX: 
TARGET_FILE_NAME: libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_FILE_DIR: <BOOST_ROOT>/lib/shared
TARGET_LINKER_FILE: <BOOST_ROOT>/lib/shared/libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_LINKER_FILE_BASE_NAME: Boost::log
TARGET_LINKER_FILE_PREFIX: 
TARGET_LINKER_FILE_SUFFIX: 
TARGET_LINKER_FILE_NAME: libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_LINKER_FILE_DIR: <BOOST_ROOT>/lib/shared

and what I would have expected:

TARGET_NAME_IF_EXISTS: Boost::log
TARGET_FILE: <BOOST_ROOT>/lib/shared/libboost_log-mgw93-mt-d-x64-1_72.dll
TARGET_FILE_BASE_NAME: boost_log-mgw93-mt-d-x64-1_72
TARGET_FILE_PREFIX: lib
TARGET_FILE_SUFFIX: .dll
TARGET_FILE_NAME: libboost_log-mgw93-mt-d-x64-1_72.dll
TARGET_FILE_DIR: <BOOST_ROOT>/lib/shared
TARGET_LINKER_FILE: <BOOST_ROOT>/lib/shared/libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_LINKER_FILE_BASE_NAME: boost_log-mgw93-mt-d-x64-1_72
TARGET_LINKER_FILE_PREFIX: lib
TARGET_LINKER_FILE_SUFFIX: .dll.a
TARGET_LINKER_FILE_NAME: libboost_log-mgw93-mt-d-x64-1_72.dll.a
TARGET_LINKER_FILE_DIR: <BOOST_ROOT>/lib/shared

That way I could easily copy the files.

Also the limited availability of string-manipulation generator expressions as already discussed prevents me from quickly replacing the CMAKE_IMPORT_LIBRARY_SUFFIX with the CMAKE_SHARED_LIBRARY_SUFFIX.

Workaround

I thought of a solution, which is not very pretty, but it works:

foreach(CONFIG_TYPE Debug Release)
	get_target_property(LIBRARY_FULL_PATH_${CONFIG_TYPE} Boost::log "LOCATION_${CONFIG_TYPE}")
	get_filename_component(LIBRARY_DIRECTORY_${CONFIG_TYPE} ${LIBRARY_FULL_PATH_${CONFIG_TYPE}} "DIRECTORY")
	get_filename_component(LIBRARY_NAME_${CONFIG_TYPE} ${LIBRARY_FULL_PATH_${CONFIG_TYPE}} "NAME_WE")						
endforeach() 

# Add a post-build command to copy all shared and import libraries
add_custom_command(TARGET ${TARGET_NAME} POST_BUILD
	# Command to copy the shared library.
	COMMAND "${CMAKE_COMMAND}" -E copy_if_different "$<IF:$<CONFIG:Debug>,${LIBRARY_DIRECTORY_Debug}/${LIBRARY_NAME_Debug},${LIBRARY_DIRECTORY_Release}/${LIBRARY_NAME_Release}>${CMAKE_SHARED_LIBRARY_SUFFIX}" "${LIBRARY_OUTPUT_DIRECTORY}"
	# Command to copy the import library.
	COMMAND "${CMAKE_COMMAND}" -E copy_if_different "$<IF:$<CONFIG:Debug>,${LIBRARY_DIRECTORY_Debug}/${LIBRARY_NAME_Debug},${LIBRARY_DIRECTORY_Release}/${LIBRARY_NAME_Release}>${CMAKE_IMPORT_LIBRARY_SUFFIX}" "${ARCHIVE_OUTPUT_DIRECTORY}" )

There is no such things as ${LIBRARY_DIRECTORY_$<CONFIG>}, right? I get this error:

Invalid character ('<') in a variable name

Is there a way to go around this? I tried this without success:

set(LIBRARY_NAME_GENEX LIBRARY_NAME_$<CONFIG>)	
...
COMMAND "${CMAKE_COMMAND}" -E echo $<GENEX_EVAL:${LIBRARY_NAME_GENEX}> # 'LIBRARY_NAME_Debug'
COMMAND "${CMAKE_COMMAND}" -E echo $<GENEX_EVAL:${${LIBRARY_NAME_GENEX}}> # '' (empty string)
...