[CMake] Dependency build order problem

[Alexander Neundorf]

On Saturday 05 January 2008, Trevor Kellaway wrote:
> Hi,
>
> I have an issue where I need to force the order some libraries are built
> in prior to building the application. Here is a simplified example (also
> attached) showing the issue (the real problem is building multiple unit
> test EXEs and running them under a nightly build using CTest):
>
> Library "e" consists of the following, with "e_auto.h" being auto
> generated:
>
>  e_auto.h
>  e.h
>  e.c
>
> Library "d" depends on the "e_auto.h" file:
>
>  Includes "e_auto.h"
>  d.h
>  d.c
>
> The application uses libraries "d.a" and "e.a".
>
> There are multiple CMakeLists in a tree:
>
>  ./source/d/CMakeLists.txt
>  ./source/e/CMakeLists.txt
>  ./source/app/CMakeLists.txt
>  ./source/CMakeLists.txt
>
> The build is being perform in ./build with the command 'CMake -G"MinGW
> Makefiles" ..\source'
>
> I can't find a way to tell CMake that library "d" depends on a
> side-effect of library "e" being built first.
>
> An obvious workaround is to change the order of the ADD_SUBDIRECTORY in
> the top level CMakeLists.txt, changing:
>
>  ADD_SUBDIRECTORY (d   ${CMAKE_BINARY_DIR}/tmp/d)
>  ADD_SUBDIRECTORY (e   ${CMAKE_BINARY_DIR}/tmp/e)
>  ADD_SUBDIRECTORY (app ${CMAKE_BINARY_DIR}/tmp/app)
>
> to
>
>  ADD_SUBDIRECTORY (e   ${CMAKE_BINARY_DIR}/tmp/e)
>  ADD_SUBDIRECTORY (d   ${CMAKE_BINARY_DIR}/tmp/d)
>  ADD_SUBDIRECTORY (app ${CMAKE_BINARY_DIR}/tmp/app)
>
> This is fine for this simple example, but my real world example is
> building multiple unit test exe files and the interdependence of them
> defeats attempts to control the build order via ADD_SUBDIRECTORY (they
> are built out of order).
>
> Of course if I manually force the "e" library target to be built prior
> to the "all" target this also works:
>
>  make e all
>
> However, I can't use this approach as the build is being performed by
> CTest and I can't control (or can I?) the build order on the command
> line for a continuous and nightly build.
>
>
> What is the right way to force this style of dependency?
>
> If I force a dependency for "d.c" on "e_auto.h":
>
> 	SET_SOURCE_FILES_PROPERTIES (d.c PROPERTIES OBJECT_DEPENDS
> ${CMAKE_BINARY_DIR}/e_auto.h)
>
> The when I make I get:
>
>  *** No rule to make target `e_auto.h'
>
> As it can't locate the ADD_CUSTOM_COMMAND in e's CMakeLists.txt from d's
> CMakeLists.txt (running from the top-level CMakeLists.txt).
>
>
> Any help greatly appreciated.

I think you have to use
add_dependencies(d e)

to tell cmake that d depends on e (which it does since it needs something from 
the build of e)

Alex