Re: Too many Recommends (in particular on mail-transport-agent)

[Christian Seiler <christian@iwakd.de>]

Hi there,

I think one of the main problems with Recommends: is not
actually the dependencies of packages themselves (I think
that most things in your list I disagree with, those
Recommends: are fine in my eyes), but rather in the way
they are handled in APT.

Let me make a couple of points (some are problems, some are
suggestions):

 - You install package A, which Recommends: B, but you don't
   want B, notice that at the time, and either remove B
   afterwards, or install A with --no-install-recommends. But
   then you install package C at a later point in time, which
   actually depends on B. You notice that C is not what you
   wanted, purge it again, but apt-get autoremove will _not_
   remove B, even though it's automatically installed, because
   A recommends it.

   So basically, the following command sequence may or may not
   leave your system in an identical state, depending on the
   packages that previously have been installed on your system:

      apt-get install A
      apt-get purge A
      apt-get autoremove --purge

   Unfortunately, I don't see a good solution to this problem,
   and I've thought about this a lot in the past.

 - When installing APT's text UI doesn't differentiate between
   extra packages that were full dependencies, and those that
   were just recommends. What would be great if APT could
   somehow show this information.

 - My guess is that most power users don't use any GUI, but
   the command line client, for installing packages. (Like I
   do.) However, it would be great if there could be some
   possibility of dropping individual Recommends even with
   the minimalistic text UI of APT.

   Example:

     # apt-get install $pkg
     Reading package lists... Done
     Building dependency tree
     Reading state information... Done
     The following additional packages will be installed:
       $pkg2 $pkg3 $pkg4
     Of these, the following only due to a recommendation:
       $pkg3 $pkg4
     Suggested packages:
       $pkg5 $pkg6
     The following NEW packages will be installed:
       $pkg $pkg2 $pkg3 $pkg4
     0 upgraded, 4 newly installed, 0 to remove and 0 not
     upgraded.
     Need to get 42 MB of archives.
     After this operation, 108 MB of additional disk space will
     be used.
     Do you want to continue? [Y/c/n]

   Where the 'c' button will first show a help (in case a more
   inexperienced user presses it accidentally) and then allow
   the user to remove packages from the list if they are pulled
   in via Recommends: - transitively or intransitively.

 - Instead of globally selecting "no recommends", it would be
   great if one could use something like apt-preferences to
   indicate that certain packages should not be installed
   unless they are manually selected _or_ they are actual hard
   Depends:-dependencies of other packages that do not fall
   in this category. Then one could for example make sure that
   -doc packages aren't installed unless they are hard
   Depends:.

 - What could also be nice would be a new dependency type that
   works like this: if the package that declares this
   dependency has been pulled in via Depends: or manually by
   the user, it should act like Recommends:, otherwise like
   Suggests:.

   For example:

      A
        Depends: B
        Recommends: C
      B:
        Depends: D
        Recommends: E
        Intransitive-Recommends: F
      C:
        Depends: G
        Recommends: H
        Intransitive-Recommends: I
      G:
        Intransitive-Recommends: J

   Then "apt-get install A" would yield the following package
   list:

      A (duh)
      B (Depends)
      C (Recommends)
      D (Depends -> Depends)
      E (Depends -> Recommends)
      F (Depends -> Intransitive-Recommends)
      G (Recommends -> Depends)
      H (Recommends -> Recommends)

   Not pulled in:

      I (Recommends -> Intransitive-Recommends)
      J (Recommends -> Depends -> Intransitive-Recommends)

   (Feel free to bikeshed over the name.)

   This could make the transitivity issue of Recommends:
   easier to deal with. Unfortunately this has some weird
   side-effects: if you mark a specific package as manually
   installed later, their Intransitive-Recommends: would need
   to change from effective Suggests: to effective Recommends:,
   which means APT somehow needs to figure out that it should
   install them. Disadvantage: APT would need to add support
   for this at the beginning of the Buster cycle, but it
   could only be used in the archive starting with Buster+1,
   otherwise upgrades from Stretch wouldn't work.

I'm not sure how good of an idea each of these is, but maybe
they could provide some inspiration for this topic.

Regards,
Christian