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

[Eric Blake <eblake@redhat.com>]

On 8/20/20 11:55 AM, 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>
> ---

In addition to reviews you already have,


> 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.

I definitely like the idea of only blowing away what we created - but if 
we created build, then recreating it for each new configure run is nice.

> 
> We could optionally symlink binaries from build/ into $PWD
> if poeople 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)'`; \

Using -maxdepth gets rid of the need to pre-create empty directories for 
nested binaries, but also loses out on binaries such as 
x86_64-softmmu/qemu-system-x86_64.  Oh, it looks like meson creates 
qemu-system-x86_64 as a binary in the top level, then a symlink in its 
old location.  Populating symlinks to ALL old locations is thus trickier 
than what you are proposing here, so it is fine to save that for a 
followup patch (let's get the bare minimum in first, so that at least 
./configure && make works, before we worry about back-compat symlinks).

> 
> This goes on top of Paolo's most recent meson port v175 posting,
> or whatever number it is upto now :-)

Nice comment for reviewers, but doesn't quite need to be preserved in git.

> 
>   .gitignore |  2 ++
>   configure  | 40 ++++++++++++++++++++++++++++++++--------
>   2 files changed, 34 insertions(+), 8 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..a5c88ad1ac 100755
> --- a/configure
> +++ b/configure
> @@ -11,6 +11,38 @@ unset CLICOLOR_FORCE GREP_OPTIONS
>   # Don't allow CCACHE, if present, to use cached results of compile tests!
>   export CCACHE_RECACHE=yes
>   
> +source_path=$(cd "$(dirname -- "$0")"; pwd)

This behaves wrong if CDPATH is set in the environment.  We should 
really include CDPATH in our environment sanitization at the top of the 
file.

> +
> +if printf %s\\n "$source_path" "$PWD" | grep -q "[[:space:]:]";
> +then
> +  error_exit "main directory cannot contain spaces nor colons"
> +fi
> +
> +if test "$PWD" == "$source_path"

bashism; s/==/=/ or you will break configure on dash systems

> +then
> +    echo "Using './build' as the directory for build output"

Do we want a way for a user to type './configure builddir=build/' and 
'make builddir=build/' so they can specify different builddir overrides 
per invocation (of course, where builddir defaults to 'build/' if not 
specified)?  But hardcoding to _just_ ./build/ for getting this patch in 
quickly is fine.

> +    rm -rf build
> +    mkdir -p build
> +    cat > GNUmakefile <<EOF

If you use 'EOF' or \EOF here, then...

> +
> +ifeq (\$(MAKECMDGOALS),)

you wouldn't have to escape all these $.  Looking through the file...

> +recurse: all
> +endif
> +
> +.NOTPARALLEL: %
> +%: force
> +	@echo 'changing dir to build for \$(MAKE) "\$(MAKECMDGOALS)"...'
> +	@\$(MAKE) -C build -f Makefile \$(MAKECMDGOALS)
> +	if test "\$(MAKECMDGOALS)" = "distclean" ; then rm -rf build ; fi
> +force: ;
> +.PHONY: force
> +GNUmakefile: ;
> +
> +EOF

...I didn't see any use of $ that was not supposed to be literally in 
the generated GNUmakefile.

> +    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

Now that we are guaranteeing configure is run in a build directory, this 
part of configure might have some cleanups possible.  But that can be a 
separate patch.

> @@ -297,14 +329,6 @@ 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"
> -fi
> -
>   # default parameters
>   cpu=""
>   iasl="iasl"
> 

Looking forward to v2.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org