Bug#1030020: apt: Conditional way to automatically uninstall Protected packages due to Build-Conflicts

[Guillem Jover <guillem@debian.org>]

Package: apt
Version: 2.5.5
Severity: wishlist

Hi!

On a thread on debian-devel, Adrian Bunk brought up the potential
problem of packages with a Build-Conflicts against a
«Protected/Important: yes» package. To me it makes sense that the
tooling should be able to cover this theoretical problem automatically,
when the build is happening on a discardable system (such as in a chroot
or an ephemeral VM). On a practical note, I think I'd find upsetting
if the particular example brought up (e2fsprogs) was to be added
as a Build-Conflicts of any package, as that pretty much means it
would be unsafe to build such package on your main system if your
filesystem is extN, and IMO that package would deserve a bug report.

I checked the code and I find in apt-pkg/deb/dpkgpm.cc the
config variable pkgCacheGen::Protected being used, but I'm not sure I
understand how it is intended to be used? The code returns true for
"none" and "native" and when the "Important" flags is not-zero, but
«doc/examples/configure-index» also mentions an "all" value which
does not seem to be handled here? Shouldn't the "none" mean to return
false?

If this is already supported by that option I'd request documentation
for it, or otherwise support for a similar option to control this
would be nice. Then a build-driver such as sbuild or pbuilder could
disable that option when and iff it knows it is driving the build
inside a discardable system.

Thanks,
Guillem