Bug#578597: Recommend usage of dpkg-buildflags to initialize CFLAGS and al.

[Goswin von Brederlow <goswin-v-b@web.de>]

Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr> writes:

> On Wed, Apr 21, 2010 at 09:10:54AM +0200, Raphael Hertzog wrote:
>> Package: debian-policy
>> Severity: wishlist
>> 
>> The desired outcome is that all package grab the values directly from
>> dpkg-buildflags and that we can stop exporting the variables from
>> dpkg-buildpackage. That way calling debian/rules directly and via
>> dpkg-buildpackage should give the same result.
>> 
>> Please modify the policy to recommend the usage of dpkg-buildflags (I would
>> suggest to push that policy change just at the start of squeeze+1).
>> 
>> CFLAGS=$(shell dpkg-buildflags --get CFLAGS)
>
> There should be some documentation about how thoses variables should be used,
> whether they should replace or augment the value set by debian/rules, before or
> after the upstream makefile change, etc...
> Currently it is impossible to use them at all in a reliable way.
>
> For example suppose debian/rules do
> CFLAGS="-O2 -Wall -g"
> and upstream configure do 
> CFLAGS="$CFLAGS -fno-strict-aliasing"
> before writing the Makefile so C files are built with
> gcc -O2 -Wall -g -fno-strict-aliasing foo.c
>
> Suppose user set CFLAGS to XXX. How C files should build ?
> gcc XXX foo.c
> gcc XXX -fno-strict-aliasing foo.c
> gcc XXX -O2 -Wall -g -fno-strict-aliasing foo.c
> gcc XXX -g -fno-strict-aliasing foo.c

User knows best and if configure just adds things to CFLAGS then that
can't be avoided in rules. So you should get:

gcc XXX -fno-strict-aliasing foo.c

> Should it depends of some properties of the package, if yes which ?
>
> Cheers,

At the moment you have the following behaviour:

% DEB_CFLAGS_SET=-O0 dpkg-buildflags --get CFLAGS
-O0
% DEB_CFLAGS_APPEND=-Werror dpkg-buildflags --get CFLAGS
-g -O2 -Werror

Maybe setting CFLAGS should behave just like setting DEB_CFLAGS_SET. But
currently that is ignored. Might be a good thing because now you can set
CFLAGS for non-debian sources without interfering with building debian
packages.

MfG
        Goswin

PS: Why can't I do 'eval $(shell dpkg-buildflags --all)'?