[RFC,v2] pkg-generic: detect incorrectly used package

In Buildroot, the selection of a package from a Config.in level and
from a Makefile level are completely disconnected. This can lead to
issues where the build of a package is triggered at the Makefile level
due to the package being listed in another package <pkg>_DEPENDENCIES
variable, even if that package is not enabled in the configuration.

This has for example been the case recently with python-can having
'python' in its <pkg>_DEPENDENCIES, while python-can could be enabled
when Python 3.x is used, in which case the 'python' package should not
be built.

To detect such issues more easily, this patch adds a check in the
package infrastructure. When the build process of a package is being
triggered, we verify that the package is enabled in the
configuration. We do this check in the "configure" step, since this
step is the first common step between the normal download case and the
"local site method" / "package override" case.

This requires passing two new target variables to the configure
target:

 - TYPE, which is either host or target. This is needed since the test
   should only be done on target packages (most host packages don't
   have a Config.in option)

 - KCONFIG_VAR, which is the name of the Config.in variable
   corresponding to the package being built. For most packages, it's
   BR2_PACKAGE_<pkg>, but not for toolchain packages, bootloaders or
   linux.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
Still sent as an RFC. Maybe we should make this optional, since it
prevents from doing "make <pkg>" when "<pkg>" is not selected in
menuconfig, which can be seen as annoying for power users. So maybe we
could enable this only in the autobuilders? But then newcomers writing
new packages would not notice their potential mistake.

Changes since v1:
 - Use KCONFIG_VAR in order to make the thing work for toolchain
   packages, bootloaders and Linux. Issue reported by Vicente.
---
 package/pkg-generic.mk | 6 ++++++
 1 file changed, 6 insertions(+)

>>>>> "Thomas" == Thomas Petazzoni <thomas.petazzoni@free-electrons.com> writes:

 > In Buildroot, the selection of a package from a Config.in level and
 > from a Makefile level are completely disconnected. This can lead to
 > issues where the build of a package is triggered at the Makefile level
 > due to the package being listed in another package <pkg>_DEPENDENCIES
 > variable, even if that package is not enabled in the configuration.

[snip]

> ---
 > Still sent as an RFC. Maybe we should make this optional, since it
 > prevents from doing "make <pkg>" when "<pkg>" is not selected in
 > menuconfig, which can be seen as annoying for power users. So maybe we
 > could enable this only in the autobuilders? But then newcomers writing
 > new packages would not notice their potential mistake.

Yes, that's indeed something I do very often. Alternatively we can
perhaps extend the logic to also check MAKECMDGOALS and only trigger for
empty / default builds.

 > index 6a7d97e..7db5ab8 100644
 > --- a/package/pkg-generic.mk
 > +++ b/package/pkg-generic.mk
 > @@ -143,6 +143,10 @@ $(foreach dir,$(call qstrip,$(BR2_GLOBAL_PATCH_DIR)),\
 
 >  # Configure
 >  $(BUILD_DIR)/%/.stamp_configured:
 > +	if test "$(TYPE)" = "target" -a -z "$($(KCONFIG_VAR))" ; then \
 > +		echo "ERROR: package $(PKG) is being built but is not enabled in the configuration." ; \
 > +		exit 1 ; \
 > +	fi

This should imho also use @.

It would be good if the error message would be more clear about what the
problem is and how to fix it. Something like:

A package must have added $(PKG) to its _DEPENDENCIES line but forgot to
add the corresponding select / depends on $(KCONFIG_VAR). Please review
your packages and try again.

Dear Peter Korsgaard,

On Sat, 29 Aug 2015 12:05:18 +0200, Peter Korsgaard wrote:

>  > Still sent as an RFC. Maybe we should make this optional, since it
>  > prevents from doing "make <pkg>" when "<pkg>" is not selected in
>  > menuconfig, which can be seen as annoying for power users. So maybe we
>  > could enable this only in the autobuilders? But then newcomers writing
>  > new packages would not notice their potential mistake.
> 
> Yes, that's indeed something I do very often. Alternatively we can
> perhaps extend the logic to also check MAKECMDGOALS and only trigger for
> empty / default builds.

That could be an option, indeed. Only enable this check if MAKECMDGOALS
is empty or "all" ?

>  > index 6a7d97e..7db5ab8 100644
>  > --- a/package/pkg-generic.mk
>  > +++ b/package/pkg-generic.mk
>  > @@ -143,6 +143,10 @@ $(foreach dir,$(call qstrip,$(BR2_GLOBAL_PATCH_DIR)),\
>  
>  >  # Configure
>  >  $(BUILD_DIR)/%/.stamp_configured:
>  > +	if test "$(TYPE)" = "target" -a -z "$($(KCONFIG_VAR))" ; then \
>  > +		echo "ERROR: package $(PKG) is being built but is not enabled in the configuration." ; \
>  > +		exit 1 ; \
>  > +	fi
> 
> This should imho also use @.

Aah, yes. I actually had a @ at some point during my development, until
the point where I had to debug this :)

> It would be good if the error message would be more clear about what the
> problem is and how to fix it. Something like:
> 
> A package must have added $(PKG) to its _DEPENDENCIES line but forgot to
> add the corresponding select / depends on $(KCONFIG_VAR). Please review
> your packages and try again.

Will fix.

Thanks for the suggestions!

Thomas