CMake - Alternative to generator expression for build output directory? - build

Question

I have a cmake build system gone wild. Before supporting IDEs, everything was ok.
I need to copy files (shaders in this case) to the build directory. They need to be copied when they've changed, regardless of whether the main target is built or not.
I had success before, as I could add a custom command with ${CMAKE_CURRENT_BINARY_DIR}, add dependencies later and everything was fine.
The problem is, when using a generator expression for the command output, it creates a dependency from my custom command to the main target. This means adding a dependency backwards (which is needed to trigger the copy) throws an error because of cyclic dependencies.
This is what I have so far, which doesn't work because the custom target (thus custom command) is not triggered when the main target doesn't need rebuilding.
set(SHADER_IN_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/shaders)
file(GLOB_RECURSE SHADERS "${SHADER_IN_DIR}/*.glsl")
add_custom_command(TARGET ${PROJECT_NAME} PRE_BUILD
COMMAND ${CMAKE_COMMAND} -E make_directory $<TARGET_FILE_DIR:${PROJECT_NAME}>/shaders/)
set(STAMP_DIR ${CMAKE_CURRENT_BINARY_DIR}/.stamps)
add_custom_command(TARGET ${PROJECT_NAME} PRE_BUILD
COMMAND ${CMAKE_COMMAND} -E make_directory ${STAMP_DIR})
set(STAMP_FILES "")
foreach(SHADER ${SHADERS})
get_filename_component(SHADER_FILENAME ${SHADER} NAME)
set(STAMP_FILE ${STAMP_DIR}/${SHADER_FILENAME}.stamp)
add_custom_command(
OUTPUT ${STAMP_FILE}
COMMAND ${CMAKE_COMMAND} -E touch ${STAMP_FILE}
COMMAND ${CMAKE_COMMAND} -E copy_if_different ${SHADER} $<TARGET_FILE_DIR:${PROJECT_NAME}>/shaders/${SHADER_FILENAME}
DEPENDS ${SHADER}
)
list(APPEND STAMP_FILES ${STAMP_FILE})
endforeach()
add_custom_target(Shaders
SOURCES ${SHADERS}
DEPENDS ${STAMP_FILES})
# Need to add dependency here! But I can't :(
So, is there any other way to get what output directory will be used in an IDE? All "solutions" I've read to force building a target have failed (they pretty much all rely on add_dependencies).
Thank you for saving my sanity.

Answer 1

In the end, instead of trying to find out where the IDE is going to output the binary, I forced output in a predictable bin/ dir.
set(BINARY_OUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/bin)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${BINARY_OUT_DIR})
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${BINARY_OUT_DIR})
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${BINARY_OUT_DIR})
foreach(OUTPUTCONFIG ${CMAKE_CONFIGURATION_TYPES})
string(TOUPPER ${OUTPUTCONFIG} OUTPUTCONFIG)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${BINARY_OUT_DIR})
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${BINARY_OUT_DIR})
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${BINARY_OUT_DIR})
endforeach(OUTPUTCONFIG CMAKE_CONFIGURATION_TYPES)