[CMake] How to depend on an ExternalProject

[Michael Wild]

On 8. Oct, 2010, at 10:50 , Rolf Eike Beer wrote:

> Hi,
> 
> I have a problem with ExternalProject and how to depend on that. I'm not
> absolutely sure I got the CMakeLists.txt right, so I first ask here before
> filing a bug report.
> 
> The idea is like this: we have an project that generates a couple of
> files. In a special configuration of another project we need those files
> as input for a special build step. Those step will take those files,
> mangle them and will generate a source file at the end. This is then added
> as usual to a library (in my example below to a executable, but that
> doesn't matter). When I run the example below I get:
> 
> [ 80%] Built target Subdir_Build
> make[2]: *** No rule to make target `Subdir_Build', needed by `main.c'. 
> Stop.
> 
> I've tested this with 2.8.2 and 2.8.3-rc2.
> 
> Put this into CMakeLists.txt
> === snip ===
> PROJECT(MaindirThing C)
> 
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8.2)
> 
> INCLUDE(ExternalProject)
> 
> ExternalProject_Add(Subdir_Build
> 		PREFIX "${CMAKE_CURRENT_BINARY_DIR}/build_subdir"
> 		SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/subdir"
> 		CMAKE_ARGS
> "-DCMAKE_INSTALL_PREFIX=${CMAKE_CURRENT_BINARY_DIR}/build_subdir/install"
> 		INSTALL_DIR "${CMAKE_CURRENT_BINARY_DIR}/build_subdir/install"
> )
> 
> ADD_CUSTOM_COMMAND(
> 	OUTPUT "main.c"
> 	COMMAND ${CMAKE_COMMAND}
> 	ARGS -E copy ${CMAKE_CURRENT_BINARY_DIR}/build_subdir/install/foo
> ${CMAKE_CURRENT_BINARY_DIR}/main.c
> 	DEPENDS Subdir_Build
> )
> 
> ADD_EXECUTABLE(simple_exe main.c)
> === snap ===
> 
> And this goes to subdir/CMakeLists.txt
> === snip ===
> PROJECT(SubdirThing NONE)
> 
> CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
> 
> FILE(WRITE ${CMAKE_CURRENT_BINARY_DIR}/foo_file "int main(void)\n{\n 
> return 0;\n}\n")
> 
> INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/foo_file DESTINATION .)
> === snap ===
> 
> Side note: I would have expected that CMAKE_INSTALL_PREFIX is set to
> INSTALL_DIR if the external project is a cmake one.
> 
> Eike

Hi Eike

Subdir_Build is a top-level target, and the custom-command can only depend on files. You need to add a custom target that depends on main.c and then add a dependency of that custom target on Subdir_Build.

HTH

Michael

--
There is always a well-known solution to every human problem -- neat, plausible, and wrong.
H. L. Mencken