[CMake] Using ExternalProject_Add when CMakeFiles.txt is not in the root directory.

[Bradley Lowekamp]

Hello,

David Cole just said the solution in another post.

You can split the project into two, with the first one being just the download step, the second is the configuration and build. This should allow you to configure the paths for your project correctly.

I need to do this for my project too. Thanks for the question to get me paying attention here, and finding the answer is another post :)

Brad

On Jul 14, 2015, at 5:14 PM, Klaim - Joël Lamotte <mjklaim at gmail.com> wrote:

> I am attempting to use ExternalDependencies_Add with the last Protobuf version (v3.0.0) which is in alpha3 (I'm using the master branch actually)[1].
> If you don't already know: contrary to previous Protobuf version, v3.x provides
> cmake scripts (and also makes CMake's FindProtobuf module unusuable if you build Protobuf using CMake BTW).
> 
> I am having trouble figuring out how to ExternalProject_add work in this case:
> the CMakeFiles.txt is not in the root directory of Protobuf sources, it is in ./cmake/ [2]
> So at build time, after download, I obviously get:
> 
> >CUSTOMBUILD : CMake error : The source directory "blahblah/install_protobuf" does not appear to contain CMakeLists.txt.
> 
> I tried several approaches using this as a base:
> 
> ExternalProject_Add( install_protobuf
>     PREFIX ${NETRUSH_DEPENDENCIES_DIR}/protobuf
>     GIT_REPOSITORY https://github.com/google/protobuf.git
>     GIT_TAG master
>    
>     CMAKE_CACHE_ARGS
>         -DBUILD_TESTING:bool=FALSE
> )
> 
> 
> I tried setting SOURCE_DIR but failed to make it work mainly because I'm
> not sure what value to set exactly, and 
> 
>    SOURCE_DIR cmake
> 
> Does not seem to work.
> 
> I was wondering if there is some args I could pass to CMake using CMAKE_ARGS
> but from the cmake[3] page in the doc I don't see anything that match exactly, or 
> I might be misunderstanding something.
> 
> I found this recommandation from Miklos Espak from 8th February 2015:
> "Specify a patch command that creates a toplevel cmake list with one 'add_subdirectory(A)'  line."
> 
> It seems to work, but it also means that the repository is modified, which is something
> I want to avoid. Also it's really a hack for passing the right working directory to cmake.
> 
> Is there a simpler way to do it that I missed?
> 
> Thanks for your time.
> 
> Joël Lamotte
> 
> 
> [1] https://github.com/google/protobuf
> [2] https://github.com/google/protobuf/tree/master/cmake
> [3] http://www.cmake.org/cmake/help/v3.3/manual/cmake.1.html#manual:cmake(1)
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