CMake: How to set dependency from executable to custom target

Question

I am using CMake on a linux environment using cmake 2.8.1. I also tried cmake 2.8.7 with the same results.

I need to do some special conditioning on an archive (static library). This is done as a cmake custom_command. The result is a new archive that should be used in the link of the executable. The input archive for the conditioning is also a cmake target.

What I need is a dependency between the conditioned version of the archive and the executable. Using add_dependencies doesn't work and I don't undestand why.

I created an example that shows that behaviour of cmake. The example contains 2 C Files, one for the archive and one containing main(). As simple archive conditioning I just make a copy of the previously generated archive.

Here are the 2 source files:

main.c:

int myPrint(void);

int main(void)
{
  myPrint();
}

mylib.c:

#include <stdio.h>

int myPrint(void)
{
  printf("Hello World\n");
}

This is the CMakeLists.txt I created:

cmake_minimum_required(VERSION 2.8)

project(cmake_dependency_test)

add_library(mylib STATIC mylib.c)

add_custom_command(OUTPUT libmylib_conditioned.a
                   COMMAND cp libmylib.a libmylib_conditioned.a
                   DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib.a
                   COMMENT "Conditioning library")
add_custom_target(conditioning DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib_conditioned.a)
add_dependencies(conditioning mylib)

add_executable(cmake_dependency_test main.c)
add_dependencies(cmake_dependency_test conditioning)
target_link_libraries(cmake_dependency_test -L. mylib_conditioned)

First I create the archive mylib. With add_custom_command I do the conditioning and add_custom_target provides a top level target for the conditioned archive. Since I need to update the input archive before the conditioned archive is built I added a dependency between the input archive top level target and the conditioned archive top level target. This works perfectly! When I touch mylib.c and run make conditioning the input archive is built and after that the conditioned archive.

Ok. Now I use the conditioned archive for linking. In order to have a dependency from the executable to the conditioned archive I used again add_dependencies. But touching the library source mylib.c and then running make will not update the executable as expected.

Where is the mistake in the CMakeLists.txt?

Answer 1

You can try to set the target property LINK_DEPENDS for the target cmake_dependency_test.

...
add_executable(cmake_dependency_test main.c )  
set_property(TARGET cmake_dependency_test PROPERTY LINK_DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib_conditioned.a)  
add_dependencies(cmake_dependency_test conditioning mylib)
target_link_libraries(cmake_dependency_test -L. mylib_conditioned)