Hi Michael and Nicola,
I'm in a similar situation as I' m trying to build up a cmake based dependency builder for OpenSceneGraph based projects:
So I' m really interested in any "best practice" advice

Michael Wild wrote:
On 17. Mar, 2010, at 13:17 , Nicola Brisotto wrote:

Hi!
I'm building a project that require a 3rd party library libqxmpp. Both project uses cmake I want to build libqxmpp with ExternalProject_add, this the code I use:

ExternalProject_add(
        libqxmpp
        #no download, i'm using git submodule
        DOWNLOAD_COMMAND ""
        CMAKE_ARGS 
-DQT_QMAKE_EXECUTABLE=/devel/BIN/v4.6.1-git-phonon-dbg-release/bin/qmake 
-DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}
        SOURCE_DIR ${CMAKE_SOURCE_DIR}/src/3rdparty/qxmpp-read-only-git/source
)
Means there is a way to instruct

ExternalProject_add

to download from GIT repos? I was not aware of and starting to hack it to 
add... let me know if one is available:
I have already added Bazaar download similarly to SVN ...  so if there is a way 
to share hacking on it


The problem arise when I try to import a target from libqxmpp adding this to my 
project CMakeLists.txt:
#Import libQXmppClient include(${CMAKE_BINARY_DIR}/include/QXmppClient/QXmppClient.cmake)

Cmake cannot find QXmppClient.cmake because it will be created when I'll build 
the project.
How can I solve this problem? Are there better solution to build and link an 
external project?

This is the libqxmpp snippet that export the target:

INSTALL(TARGETS QXmppClient EXPORT QXmppClient DESTINATION lib)
INSTALL(EXPORT QXmppClient DESTINATION include/QXmppClient )
Sorry my ignorance, this is part of the install step of  QXmppClient ?

Nicola Brisotto
vcard

There are two ways of getting around this:

1) create the IMPORTED targets yourself.

2) also build your main project wit a ExternalProject_Add and drive the whole thing from 
a "master-CMakeLists.txt"

The first one is probably easier to set up, but requires you to guess the 
installation names and paths correctly. The second option requires you to 
restructure your whole build system and adds considerable complexity due to the 
communication between your master-project and the external projects. For this 
communication I'd try the following:

- In the master project do all the feature-detection and setting of cache 
variables (such as options etc)
- Write a cache-initializer script to the binary tree
- Do all the ExternalProject_Add calls and specify the cache-initializer script 
with the -C option in CMAKE_ARGS
This suggestion is really interesting: the purpouse is to let any config options in the "master" projects to be passed to the "slaves"?
Have you any examples?


I came up with a schema like 2:
any project is built as external, dependencies are resolved by ExternalProject_Add and I have used CMAKE_ARGS to communicate settings: As most of cmake projects were based on FindXXX stuff for finding deps, I have overridden the necessary modules in order to make the projects find the good components at configure time.

As I did not yet need a lot of interactive customization, I just passed common parameters using CMAKE_ARGS


Would not something similar work for you:
keep your project separate from libqxmpp, add to it a find_package(QXmppClient)
then build a "master" project where you do:

ExternalProject_add(
        libqxmpp
        #no download, i'm using git submodule
        DOWNLOAD_COMMAND ""
        CMAKE_ARGS 
-DQT_QMAKE_EXECUTABLE=/devel/BIN/v4.6.1-git-phonon-dbg-release/bin/qmake 
-DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}
        SOURCE_DIR ${CMAKE_SOURCE_DIR}/src/3rdparty/qxmpp-read-only-git/source
)



ExternalProject_Add(<your_project_name>
   DEPENDS libqxmpp
   DOWNLOAD_COMMAND ""
   SOURCE_DIR ${CMAKE_SOURCE_DIR}/<your project subsource dir>
   INSTALL_DIR ${CMAKE_INSTALL_PREFIX}


HTH
          Luigi




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