[cmake-developers] ExternalProject: adding command line flags for CMAKE_MAKE_PROGRAM

[Brad King]

On 07/30/2014 11:06 AM, Williams, Norman K wrote:
> I was trying to get ExternalProjects generated with the Ninja
> generator to do a better job of handling multiple CPUs and load,
> so I tried the naïve solution below.

For reference in the archives, your previous post about this was here:

 CMake, Ninja generator, and ExternalProjects
 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/10543

> I needed to add flags to the program named in CMAKE_MAKE_PROGRAM.

The relevant part of the ExternalProject module source is the block
that constructs the default BUILD_COMMAND when not using a Makefile
generator:

        # Drive the project with "cmake --build".
        get_target_property(cmake_command ${name} _EP_CMAKE_COMMAND)
        if(cmake_command)
          set(cmd "${cmake_command}")
        else()
          set(cmd "${CMAKE_COMMAND}")
        endif()
        set(args --build ${binary_dir} --config ${CMAKE_CFG_INTDIR})

At build time, "cmake --build" loads the CMAKE_MAKE_PROGRAM from the
CMakeCache.txt of the build tree, at least for the Ninja generator.
When running "cmake --build" by hand one can specify additional args:

 cmake --build . -- $ExtraArgs

Everything after the "--" option will be given to the native tool.

Perhaps one could add a special-case here when cmake_generator is
"Ninja" to extend the "cmake --build" command with th needed options
to ninja.

> the only alternative is to explicitly set the BUILD_COMMAND for
> every ExternalProject_add command.

That would also work with existing CMake releases, but would have
to be conditional on the generator in use.

-Brad