[OE-core] [PATCH] cmake.bbclass: make cleaning of build directory on configure optional

[Richard Purdie]

On Thu, 2019-01-17 at 11:51 +1300, Douglas Royds wrote:
> From: Sam Nobs <samuel.nobs at taitradio.com>
> 
> The do_configure task is sensitive to changes in recipes and
> configuration files.
> This can be time consuming because cmake.bbclass deletes the ${B}
> directory
> at the beginning of the do_configure task. CMake figures
> out what to do when it's run again, so unless your cmake files are
> buggy, there shouldn't
> be any need to erase the build directory and start afresh.
> 
> This change allows you to turn this behaviour off, either globally or
> on a per-recipe basis, e.g.
> 
> OECMAKE_CLEAN_BUILDDIR_ON_CONFIGURE_pn-yourrecipe = ""
> 
> Signed-off-by: Sam Nobs <samuel.nobs at taitradio.com>
> ---
>  meta/classes/cmake.bbclass | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)

This may give a speed boost for some cases but it does come at a
potential risk of determinism issues.

I appreciate you've made it configurable but that actually further
concerns me as we now have two code paths which potentially both have
to be tested.

Is this change really worth it?

Cheers,

Richard

> diff --git a/meta/classes/cmake.bbclass b/meta/classes/cmake.bbclass
> index fa7f68c99b..b9ec68ac9a 100644
> --- a/meta/classes/cmake.bbclass
> +++ b/meta/classes/cmake.bbclass
> @@ -63,6 +63,11 @@ EXTRA_OECMAKE_BUILD_prepend_task-install =
> "${PARALLEL_MAKEINST} "
>  OECMAKE_TARGET_COMPILE ?= "all"
>  OECMAKE_TARGET_INSTALL ?= "install"
>  
> +# Clean the build directory before configuring.
> +# Some recipes don't want/need this as cmake is perfectly
> +# capable of figuring out what to do, so we allow it to be turned
> off
> +OECMAKE_CLEAN_BUILDDIR_ON_CONFIGURE ??= "true"
> +
>  # CMake expects target architectures in the format of uname(2),
>  # which do not always match TARGET_ARCH, so all the necessary
>  # conversions should happen here.
> @@ -133,12 +138,20 @@ cmake_do_configure() {
>  		bbnote "cmake.bbclass no longer uses
> OECMAKE_BUILDPATH.  The default behaviour is now out-of-tree builds
> with B=WORKDIR/build."
>  	fi
>  
> -	if [ "${S}" != "${B}" ]; then
> -		rm -rf ${B}
> -		mkdir -p ${B}
> -		cd ${B}
> +	if [ ${@oe.types.boolean('${OECMAKE_CLEAN_BUILDDIR_ON_CONFIGURE
> }')} = True ]; then
> +		if [ "${S}" != "${B}" ]; then
> +			rm -rf ${B}
> +			mkdir -p ${B}
> +			cd ${B}
> +		else
> +			# For an in-tree build, delete all object files
> and CMake artefacts
> +			find ${B} -name CMakeFiles -or -name Makefile
> -or -name cmake_install.cmake -or -name CMakeCache.txt -delete
> +		fi
>  	else
> -		find ${B} -name CMakeFiles -or -name Makefile -or -name
> cmake_install.cmake -or -name CMakeCache.txt -delete
> +		# Selectively delete CMake artefacts to ensure that -c
> configure has a consistent result
> +		rm -f CMakeCache.txt
> +		cmake_version=$(cmake --version | head -1 | sed
> 's#^[^0-9]*\([0-9.]*\).*$#\1#' )
> +		rm -fr CMakeFiles/$cmake_version/
>  	fi
>  
>  	# Just like autotools cmake can use a site file to cache result
> that need generated binaries to run
> -- 
> 2.17.1
>