Re: [PATCH v2] configure: add support for pseudo-"in source tree" builds

[Philippe Mathieu-Daudé]

On 8/20/20 7:31 PM, Daniel P. Berrangé wrote:
> Meson requires the build dir to be separate from the source tree. Many
> people are used to just running "./configure && make" though and the
> meson conversion breaks that.
> 
> This introduces some backcompat support to make it appear as if an
> "in source tree" build is being done, but with the the results in the
> "build/" directory. This allows "./configure && make" to work as it
> did historically, albeit with the output binaries staying under build/.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
> 
> This is a simple integration of Eric's proposal from
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2020-03/msg07290.html
> 
> with a bit of configure magic. It is enough to enable
> 
>    ./configure
>    make
>    make check
> 
> I've not tested it beyond that. Note it blows away the "build/"
> dir each time ./configure is run so it is pristine each time.
> 
> We could optionally symlink binaries from build/ into $PWD
> if people think that is important, eg by changing GNUmakefile
> to have:
> 
> recurse: all
>         for bin in `find build -maxdepth 1 -type f -executable | grep -v -E 
> '(ninjatool|config.status)'`; \
>         do \
>           ln -f -s $$bin . ; \
>         done
> 
> and some cleanup logic to purge the symlinks for "make clean"
> 
> This goes on top of Paolo's most recent meson port v175 posting,
> or whatever number it is upto now :-)
> 
> In v2:
> 
>  - Use a marker file so we don't blow away a build/ dir
>    we didn't create
>  - Silence the distclean rule
>  - Fix broken use of error_exit that's not defined yet
>  - Add comment to GNUmakefile
> 
>  .gitignore |  2 ++
>  configure  | 48 +++++++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 47 insertions(+), 3 deletions(-)
> 
> diff --git a/.gitignore b/.gitignore
> index 92311284ef..4ccb9ed975 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -1,3 +1,5 @@
> +/GNUmakefile
> +/build/
>  /.doctrees
>  /config-devices.*
>  /config-all-devices.*
> diff --git a/configure b/configure
> index cc5f58f31a..cdffe221c7 100755
> --- a/configure
> +++ b/configure
> @@ -11,6 +11,51 @@ unset CLICOLOR_FORCE GREP_OPTIONS
>  # Don't allow CCACHE, if present, to use cached results of compile tests!
>  export CCACHE_RECACHE=yes
>  
> +# make source path absolute
> +source_path=$(cd "$(dirname -- "$0")"; pwd)
> +
> +if test "$PWD" == "$source_path"
> +then
> +    echo "Using './build' as the directory for build output"
> +
> +    MARKER=build/auto-created-by-configure
> +
> +    if test -e build
> +    then
> +     if test -f $MARKER
> +     then
> +        rm -rf build
> +     else
> +         echo "ERROR: ./build dir already exists and was not previously 
> created by configure"
> +         exit 1

Tested normal build in fresh clone, then in my current workdir:

./configure
Using './build' as the directory for build output
ERROR: ./build dir already exists and was not previously created by
configure

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> +     fi
> +    fi
> +
> +    mkdir build
> +    touch $MARKER
> +
> +    cat > GNUmakefile <<EOF
> +# This file is auto-generated by configure to support in-source tree
> +# 'make' command invokation
> +
> +ifeq (\$(MAKECMDGOALS),)
> +recurse: all
> +endif
> +
> +.NOTPARALLEL: %
> +%: force
> +     @echo 'changing dir to build for \$(MAKE) "\$(MAKECMDGOALS)"...'
> +     @\$(MAKE) -C build -f Makefile \$(MAKECMDGOALS)
> +     @if test "\$(MAKECMDGOALS)" = "distclean" && test -e 
> build/auto-created-by-configure ; then rm -rf build GNUmakefile ; fi
> +force: ;
> +.PHONY: force
> +GNUmakefile: ;
> +
> +EOF
> +    cd build
> +    exec $source_path/configure "$@"
> +fi
> +
>  # Temporary directory used for files created while
>  # configure runs. Since it is in the build directory
>  # we can safely blow away any previous version of it
> @@ -297,9 +342,6 @@ ld_has() {
>      $ld --help 2>/dev/null | grep ".$1" >/dev/null 2>&1
>  }
>  
> -# make source path absolute
> -source_path=$(cd "$(dirname -- "$0")"; pwd)
> -
>  if printf %s\\n "$source_path" "$PWD" | grep -q "[[:space:]:]";
>  then
>    error_exit "main directory cannot contain spaces nor colons"
>