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

[Thomas Petazzoni]

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 at 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(+)

diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk
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 $(PKG) is being built but is not enabled in the configuration." ; \
+		exit 1 ; \
+	fi
 	@$(call step_start,configure)
 	@$(call MESSAGE,"Configuring")
 	$(foreach hook,$($(PKG)_PRE_CONFIGURE_HOOKS),$(call $(hook))$(sep))
@@ -664,6 +668,8 @@ $$($(2)_TARGET_INSTALL_IMAGES):		PKG=$(2)
 $$($(2)_TARGET_INSTALL_HOST):           PKG=$(2)
 $$($(2)_TARGET_BUILD):			PKG=$(2)
 $$($(2)_TARGET_CONFIGURE):		PKG=$(2)
+$$($(2)_TARGET_CONFIGURE):		TYPE=$(4)
+$$($(2)_TARGET_CONFIGURE):		KCONFIG_VAR=$$($(2)_KCONFIG_VAR)
 $$($(2)_TARGET_RSYNC):                  SRCDIR=$$($(2)_OVERRIDE_SRCDIR)
 $$($(2)_TARGET_RSYNC):                  PKG=$(2)
 $$($(2)_TARGET_PATCH):			PKG=$(2)
-- 
2.5.0