[Debconf-devel] Bug#779920: debconf: questions sourced from a template owned by another package block purge/install of other package

Fri Mar 6 12:38:05 UTC 2015

Package: debconf
Version: 1.5.24
Severity: normal
Control: blocks 578960 by -1

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dbconfig-common can not be purged and reinstalled correctly without
purging all reverse dependent packages. This has been reported against
dbconfig-common a long time ago (578960 and merged bugs), but I don't
believe that the bug is actually in dbconfig-common. To prevent the
the bug list of debconf to be "poluted" by the duplicates I file a new
bug against debconf which can just be closed if you really think this
is something that dbconfig-common should work around itself.

(Analysis from bug 578960 by Sean Finney) This is what happens:

dbconfig-common installs a collection of templates.  Example from
debconf config.dat cache file:

 Name: dbconfig-common/database-type 
 Template: dbconfig-common/database-type
 Owners: dbconfig-common

Later, someone installs a webapp (say, phpbb3), which registers a subset
of these packages from dbconfig-common.  Relevant entries in debconf
cache file:

 Name: dbconfig-common/database-type 
 Template: dbconfig-common/database-type
 Owners: dbconfig-common

 Name: phpbb3/database-type
 Template: dbconfig-common/database-type
 Value: 
 Owners: phpbb3
 Variables:
  database_types = mysql, pgsql, sqlite
  pkg = phpbb3

Later, both packages are removed, and even later dbconfig-common is
purged (but not phpbb3).  config.dat cache now contains:

 Name: phpbb3/database-type
 Template: dbconfig-common/database-type
 Value: 
 Owners: phpbb3
 Variables:
  database_types = mysql, pgsql, sqlite
  pkg = phpbb3

And the template still exists in templates.dat

And even later, dbconfig-common is reinstalled.  However, config.dat
cache is the same as before (i.e. no dbconfig-common/database-type ).

I'm guessing that the un-purged package with the registered copy of the
template is preventing dbconfig-common from properly setting up its own
debconf-stuff, and as pointed out it requires purging not just
dbconfig-common but all dbconfig-common using packages in order to get a
working behavior again.