Re: Pre-Depends: dpkg (>= 1.15.7.2) for dpkg-maintscript-helper okay?

[Jonathan Nieder <jrnieder@gmail.com>]

To recap, there was some discussion about whether a versioned
Pre-Depends on dpkg-maintscript-helper [dpkg (>= 1.15.7.2)] is a good
idea for packages in wheezy, with no definite conclusion.

The main complication was such Pre-Depends are not needed for
squeezy-to-wheezy upgrades.  Still I believe adding one to the git
package in wheezy would be a good thing, so I'll ask again for your
advice.  (Best of all if it comes with an explanation that can be used
to update debian-policy and save the next person from having to ask on
-devel again.)

Reasons mentioned *not* to add such a pre-dependency:

 - a smaller Packages file;
 - fewer entries in hashtables listing all dependencies;
 - fewer iterations in loops over dependencies, etc;
 - we discourage Pre-Depends in general:
   . Pre-Depends can complicate upgrade paths by constraining
     unpack order;
   . Pre-Depends can complicate upgrade paths by constraining
     configuration order;
   . Pre-Depends loops are unbreakable

However, most of those are not very problematic in the case at hand
(dependencies in wheezy on dpkg-maintscript-helper).

 - it is not obvious that kind of micro-optimization of dependency lists
   is worth much in decreasing the size of Packages and pkgcache.bin;
 - because dpkg is essential and the required version is already in
   squeeze, the kind of pre-dependency being considered does not
   complicate the squeeze-to-wheezy upgrade path.

Reasons mentioned to add a pre-dependency:

 - derivatives with different release schedules (e.g., Ubuntu LTS) would
   be able to reuse the package without changing it;
 - people installing git from sid on lenny systems wouldn't find preinst
   mysteriously failing.  Such an operation is not guaranteed to work
   but why not help out when it's this easy?
 - private backports are likely to leave out the pre-depends by mistake
   if we don't add it;

Does that seem like a fair summary?  Alternatively, what advice would
you give to a packager that wants to (reliably) remove a conffile in
wheezy?

Thanks again for your help.
Jonathan