[CMake] External library dependency

[Magnus Johansson]

We have a similar situation and the following works well enough for us:

ExternalProject_Add(
   big_external_project
   ...
)

set(OUTPUT_FILES files generated by the external build here)
set_source_files_properties(${OUTPUT_FILES} PROPERTIES GENERATED true)

add_library(internal_library ${OUTPUT_FILES} and whatever else it 
depends on)
add_dependencies(internal_library big_external_project)

Once it has been built, the big_external_project rarely gets rebuilt 
unless we do a rm -rf * in the build tree.

Magnus


On 09/19/2013 07:31 PM, Weatherby,Gerard wrote:
>
> We have an external library which is not easily "cmakeable" and takes 
> a long time to compile. We have a static copy of the source in our 
> SCCS, so we don't need to fetch etc.
>
> What we'd like to have happen is have the code compile if and only if 
> the output libraries are not present.  The best I've come up with is:
>
>                add_custom_command(OUTPUT ${CHOMBO_LIBS_2D}
>
>                               PRE_BUILD
>
>                               COMMAND ${CHOMBO_BUILD_CMD}
>
> #                            DEPENDS don't add depends line ... causes 
> recompiling of Chombo every time
>
> WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}/Chombo/lib
>
>                )
>
>                # include the Chombo libraries as "source" file to 
> trigger building them via "add_custom_command"
>
>                # if they don't exist
>
>                add_executable(${EXE_2D} ${CHOMBO_LIBS_2D} ${SRC_FILES})
>
> where CHOMBO_LIBS_2D are the libraries generated by CHOMBO_BUILD_CMD. 
> The libraries link in the source tree.
>
> This works, mostly. It doesn't work with parallel builds (make --j9)
>
> I tried looking at ExternalProject_Add but didn't seem how to tell it 
> what output is generated by the command (and hence I'm not sure how / 
> if it can be used to only make if the libraries are missing).
>
> Gerard Weatherby
>
> Appllication Architect
>
> Virtual Cell, Center for Cell Analysis and Modeling (CCAM)
>
> University of Connecticut Health Center
>
> 860-679-2065
>
>
>
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-- 
Magnus Johansson
Developer, Fox Technologies

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