[cmake-developers] CMake strips MAKEFLAGS from environment

[Ben Boeckel]

On Thu, May 21, 2015 at 09:31:41 -0400, Taylor Braun-Jones wrote:
> So I added another workound for that:
> 
>   if(${CMAKE_GENERATOR} MATCHES ".* Makefiles$")
>     set(environment_build_flags "$ENV{MAKEFLAGS}")
>   endif()
> 
>   add_custom_target(coverage_data
>     COMMAND env --unset=MAKEFLAGS ${bullseye_environment}
>       ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR} --clean-first --
> ${environment_build_flags}
>     COMMAND env ${bullseye_environment} ${CMAKE_CTEST_COMMAND}
> --output-on-failure
>     COMMENT "Generating test coverage data"
>     VERBATIM
>     )
> 
> Which allows the parallelism to work properly in an environment like:
> 
> export MAKEFLAGS=$(grep -i -c ^processor /proc/cpuinfo)
> make coverage_data

The problem with MAKEFLAGS is that `-i` also gets inherited and that is
not acceptable to use when running things like try_compile since it
causes false positives (e.g., detecting NEON extensions on x86). CMake
clears it so that it has a better expectation of how things will run. Is
there a reason you can't use a CMake cache variable to set
`environment_build_flags` rather than the environment (since it would
get remembered between cmake runs while the environment needs to be
specified every time)?

--Ben