Bug#728317: apt ignores build-conflicts on virtual package

[Johannes Schauer <j.schauer@email.de>]

Package: apt
Version: 0.9.12.1
Severity: normal

Hi,

To reproduce:

$ sudo debootstrap sid debian-sid-20131028 http://snapshot.debian.org/archive/debian/20131028T000000Z/
[...]
$ echo deb-src http://snapshot.debian.org/archive/debian/20131028T000000Z/ sid main | sudo tee -a debian-sid-20131028/etc/apt/sources.list
[...]
$ sudo chroot debian-sid-20131028 apt-get update
[...]
$ sudo chroot debian-sid-20131028 apt-cache showsrc gcc-4.6 | grep Build-Conflicts
Build-Conflicts: binutils-gold
$ sudo chroot debian-sid-20131028 apt-cache show binutils | grep Provides
Provides: binutils-gold, elf-binutils
$ sudo chroot debian-sid-20131028 apt-get build-dep --simulate gcc-4.6 | grep binutils
  autoconf autoconf2.64 autogen autotools-dev binutils bison build-essential
Inst binutils (2.23.90.20131017-1 Debian:unstable [amd64])
Conf binutils (2.23.90.20131017-1 Debian:unstable [amd64])
$ echo $?
0

The same works for src:gcc-4.7 and src:gcc-4.8.

The problem is, that gcc-4.6 Build-Conflicts with binutils-gold. The binutils
package provides binutils-gold. With my understanding of policy sections 3.6
but especially 7.5 on virtual packages, I think that apt is not supposed
to allow the compilation of a source package (here: gcc-4.6) together
with a binary package (here: binutils) providing a package that the
source package conflicts with (here: binutils-gold).

And indeed after `apt-get source`-ing the code and `apt-get
build-dep`-ing the dependencies, dpkg-checkbuilddeps prints:

dpkg-checkbuilddeps: Build conflicts: binutils-gold

cheers, josch