Bug#830574: Unable to purge a removed package if its' architecture is different from the candidate's one

[Алексей Шилин <rootlexx@mail.ru>]

Package: apt
Version: 1.0.9.8.3

Summary
--------

When purging a removed-but-not-purged package, apt is picking the candidate version instead --
and fails if the latter has a different architecture.


Details
--------

Due to iceweasel -> firefox-esr migration in stable, I removed iceweasel and installed firefox-esr
(which is faster than performing a dist-upgrade, removing transitional iceweasel packages and
marking firefox-esr as manually installed). Later I decided to purge iceweasel to get rid of now
obsolete /etc/iceweasel tree, but got this:

# apt-get purge iceweasel -y
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  iceweasel*
0 upgraded, 0 newly installed, 1 to remove and 6 not upgraded.
After this operation, 0 B of additional disk space will be used.
dpkg: warning: ignoring request to remove iceweasel which isn't installed
#

Here is how apt called dpkg:

/usr/bin/dpkg --status-fd 15 --force-depends --force-remove-essential --purge iceweasel:all

However:

# dpkg -s iceweasel | grep -E '^(Status|Version|Arch)'
Status: deinstall ok config-files
Architecture: i386
Version: 38.8.0esr-1~deb8u1
#

So it's iceweasel:i386 which should be purged, but apt picked iceweasel:all instead. This output
gives a clue, why:

# apt-cache policy iceweasel
iceweasel:
  Installed: (none)
  Candidate: 45.2.0esr-1~deb8u1
  Version table:
     45.2.0esr-1~deb8u1 0
        500 http://security.debian.org/ jessie/updates/main i386 Packages
     38.8.0esr-1~deb8u1 0
        500 http://http.debian.net/debian/ jessie/main i386 Packages
        500 http://security.debian.org/ jessie/updates/main i386 Packages
        100 /var/lib/dpkg/status
# apt-cache show iceweasel | grep -E Version\|Arch
Version: 45.2.0esr-1~deb8u1
Architecture: all
Version: 38.8.0esr-1~deb8u1
Architecture: i386
#

So iceweasel:all is the candidate version.

Explicit specification of the correct architecture (i.e. `apt-get purge iceweasel:i386') doesn't work.


Reproduction
-------------

In order to simplify reproduction of this bug, I've created a fake bar package (attached) with
`Architecture: all', which installs /etc/fakebar conf-file. Also, there is a real bar package in the
archive with the same architecture as the host one.

Steps to reproduce:
 1. Install the attached package.
 2. Run `apt-get remove bar'.
 3. Run `apt-get purge bar'.

The last one fails because instead of the fake bar apt tries to purge the real one, which has
a different architecture.


-- 
Алексей Шилин

Attachment: bar_1.0_all.deb
Description: Binary data