Add dependencies to a custom target - cmake

Question

I need a way to add additional dependencies to a custom target. I have a macro which adds resource files to a particular project, used like this:
ADD_RESOURCES( ${TARGET} some/path pattern1 pattern2 )
ADD_RESOURCES( ${TARGET} another/path pattern1 )
I create a target called ${TARGET}_ASSETS and would like to attach the generation of all these resources to the one target. add_dependencies however only accepts other targets. So if I produce a file via a add_custom_command I cannot use that as a dependency.
The workaround might be to just create a new custom taget for each call to ADD_RESOURCES and then attached that to the ASSETS target. Each target requires a unique name however, and these is no way to generate this unique name from the parameters of ADD_RESOURCES.

Answer 1

One work-around is to postpone the generation of the ${target}_ASSETS custom targets until all dependencies have been set up with calls to ADD_RESOURCES.
Instead of immediately adding the dependencies to the custom target, the macro ADD_RESOURCES has to record the dependencies in a global variable, whose name depends on the target:
macro (ADD_RESOURCES _targetName)
set (_dependencies ${ARGN})
...
# record depencies in a target dependency variable
if (DEFINED ${_targetName}_Dependencies)
list (APPEND ${_targetName}_Dependencies ${_dependencies})
else()
set (${_targetName}_Dependencies ${_dependencies})
endif()
endmacro()
Then add another helper macro which determines all defined target dependency variables through reflection and sets up a custom target for each target:
macro (SETUP_ASSETS_TARGETS)
get_cmake_property(_vars VARIABLES)
foreach (_var ${_vars})
if (_var MATCHES "(.+)_Dependencies")
set (_targetName ${CMAKE_MATCH_1})
set (_targetDependencies ${${_var}})
message("${_targetName} depends on ${_targetDependencies}")
add_custom_target(${_targetName}_ASSETS DEPENDS ${_targetDependencies})
endif()
endforeach()
endmacro()
In your CMakeLists.txt add all necessary dependencies with calls to ADD_RESOURCES, then call the SETUP_ASSETS_TARGETS macro to have all custom targets defined.
ADD_RESOURCES( target1 some/path pattern1 pattern2 )
ADD_RESOURCES( target1 another/path pattern1 )
ADD_RESOURCES( target2 foo/bar pattern1 )
...
...
SETUP_ASSETS_TARGETS()

Answer 2

I know this is a late answer, but i post my solution for everyone who searches for this problem:
function(target_resources THIS)
if (NOT TARGET ${THIS}_res)
# this is just a pseudo command which can be appended later
add_custom_command(OUTPUT ${THIS}_dep COMMAND cd ${CMAKE_CURRENT_SOURCE_DIR})
# add a dependency with a target, as a command itself can not be a dependency
add_custom_target(${THIS}_res DEPENDS ${THIS}_dep)
add_dependencies(${THIS} ${THIS}_res)
endif ()
get_target_property(RUNTIME_OUTPUT_DIRECTORY ${THIS} RUNTIME_OUTPUT_DIRECTORY)
foreach (RES_FILE IN LISTS ARGN)
if (IS_ABSOLUTE ${RES_FILE})
file(RELATIVE_PATH PATH ${CMAKE_CURRENT_SOURCE_DIR} ${RES_FILE})
endif ()
# append the resource command with our resource
add_custom_command(OUTPUT ${THIS}_dep
COMMAND ${CMAKE_COMMAND} -E copy
${CMAKE_CURRENT_SOURCE_DIR}/${RES_FILE}
${RUNTIME_OUTPUT_DIRECTORY}/${RES_FILE}
APPEND)
endforeach ()
endfunction()
The benefit of this solution is that is does not rely on global variables nor the need to invoke a setup macro.