[CMake] ExternalProject and clean targets

[David Cole]

On Sat, Oct 15, 2011 at 3:48 AM, Michael Hertling <mhertling at online.de> wrote:
> On 10/12/2011 10:22 PM, Lori Pritchett-Sheats wrote:
>>
>> I'm building external packages in my CMake system using the
>> ExternalPackages_Add function. When a package is built this way and I
>> execute a 'make clean' at the top of my build tree,  all targets are
>> cleaned including the external packages. Is there a way to remove the
>> external package targets from the the default clean target?
>
> The following exemplary project does not exhibit this behavior:
>
> # CMakeLists.txt:
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(CLEAN C)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
> INCLUDE(ExternalProject)
> ExternalProject_Add(external
>    SOURCE_DIR ${CMAKE_SOURCE_DIR}/external
>    CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>)
> FILE(WRITE ${CMAKE_BINARY_DIR}/main.c "int main(void){return 0;}\n")
> ADD_EXECUTABLE(main main.c)
> ADD_DEPENDENCIES(main external)
> INSTALL(TARGETS main DESTINATION bin)
>
> # external/CMakeLists.txt:
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(EXTERNAL C)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
> FILE(WRITE ${CMAKE_BINARY_DIR}/f.c "void f(void){}\n")
> ADD_LIBRARY(f SHARED f.c)
> INSTALL(TARGETS f DESTINATION lib)
>
> After configuring and building:
>
> % ls main external-prefix/src/external-build/libf.so
> external-prefix/src/external-build/libf.so  main
>
> After "make clean" in CMAKE_BINARY_DIR:
>
> % ls main external-prefix/src/external-build/libf.so
> ls: cannot access main: No such file or directory
> external-prefix/src/external-build/libf.so
>
> The top-level project's target is gone whereas the external project's
> one is intact, and [1] reports the same, i.e. the opposite of your
> concern. Thus, could you boil down your issue to a minimal but
> self-contained example for further investigation?
>
> Regards,
>
> Michael
>
> [1] http://www.mail-archive.com/cmake@cmake.org/msg35411.html
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When Lori said "all targets are cleaned including the external
packages" I think she meant that she would like the ExternalProject
stamp files to remain intact across a "clean" such that the
ExternalProject steps do not re-execute on the next make. Is that
indeed what you meant, Lori?

If so, I do not know of an easy way to achieve that goal.

One thing that comes to mind is separating out the parts that you
don't want to re-build after a clean into a separate project, and
build/[install] that into a place where you can reference the
built/installed products from a second project in which you frequently
'clean'...

Another alternative would be to avoid the top-level clean altogether,
and simply go down into an individual external project's build tree
and do the make clean in there so as to only clean the individual
project you're immediately working with.

I've frequently thought we should cache/share ExternalProject builds
across other multiple builds that could reference them.... but I
hesitate to put legs on that idea because of possibly introducing easy
ways to create giant tangled messes of projects with incompatible
compiler/linker flags. It's worth keeping on the idea pile, though,
and a motivated individual could certainly already achieve this by
placing the build/install products of ExternalProject_Add calls in
shared locations (i.e., in the HOME directory instead of as
sub-directories of the present build tree).


HTH,
David