In order to select packages from a variety of sources, pkg(5) supports
the configuration of multiple publishers.  We've started with the
concept of a preferred publisher, but some ambiguity has arisen as to
what should happen when publishers are deleted, added, etc.  In
addition, the single level of selection afforded by the preferred
designation appears to be somewhat limiting; at the same time, the
rules for selecting amongst multiple publishers of the same package
need clarification rather than additional complexity.

We propose the idea of publisher search order, starting with the
preferred publisher.  Adding a publisher adds a new publisher at the
end of the search order; if a publisher is made preferred it is moved
to the front of the search order.  Deleting or disabling a publisher
causes it to be removed from the search order. Re-enabling a publisher
causes it to added at the end of the search order.

When a package is nominated for installation without an explicit
publisher being specified, the first publisher found in the search
order to provide the package is selected. Once installed, subsequent
updates to that package by default always occur from that publisher,
even if a publisher earlier in the search order starts publishing a
package with the same name.  This behavior of a publisher is
characterized as "sticky", and is the default.  It can be disabled on
a per-publisher basis, and such disablement is useful mostly for
developers seeking to replace a portion of their packages w/
development versions. If a publisher is made "non-sticky", its
packages are searched for as on initial installation on every update -
no preference is afforded by the previous installation.  Deleted/disabled
publishers are made non-sticky.

Each selection of the publisher for a package is made independently
according to the algorithms above; there is no implicit inheritance
of publisher across dependencies of any type.

The above suggests the following additions to the set-publisher
subcommand of pkg:

set-publisher [--search-before=publisher] [--search-after=publisher] publisher
set-publisher [--sticky] [--non-sticky] publisher


--search-before=publisherB publisherA causes publisher A to be moved
from its current place in the search order to be just ahead of publisher B.

--search-after=publisherB publisherA causes publisher A to be moved
from its current place in the search order to be just behind publisher B.

Specifying --non-sticky causes this publisher not to automatically
be selected for all updates to packages already installed from this
publisher; instead, publishers searched earlier are automatically preferred.
--sticky causes the original behavior to be restored for subsequent
updates.


Use cases
---------

Normal user getting packages from pkg.opensolaris.org and datahavens.org:

   1) Installs system as per usual, points preferred to usual
      best available publisher - say, pkg.opensolaris.org
   2) Adds new publisher datahavens.org to acquire mplayer.
      Without specifying search order, new publisher is appended
      to the current order.

Project Developer:

   1) Installs system as per usual, points preferred to usual
      best available publisher - say, pkg.opensolaris.org
   2) Adds new publisher "MyOwnRepo" pointing at his
      latest and greatest bits. Note that his repo is lowest 
      in search order, but since his package names are unique no issues 
      arise.

Contrib User that prefers supported bits:

   1) Installs system as per usual, points preferred to usual
      best available publisher - say, pkg.opensolaris.org
   2) Adds contrib repo after p.o.o, and makes it non-sticky.
   3) Adds packages from contrib as desired.
   4) When and if packages move to p.o.o, they're automatically
      updated from p.o.o on the next image update or
      pkg install ....

OpenSolaris developer:

   1) Installs system as per usual, points preferred to usual
      best available publisher - say, pkg.opensolaris.org/dev
   2) Adds new preferred publisher "MyOwnRepo" pointing at his
      latest and greatest bits; making it preferred places it 
      first in the search order.
   3) Pkg.opensolaris.org is made non-sticky to cause pkgs from MyOwnRepo
      to replace those from pkg.opensolaris.org on next update
   4) If additional fresh bits are required, additional development
      repos can be added and placed ahead of pkg.opensolaris.org
      in the search order; in this way multiple consolidations 
      can be kept at the bleeding edge.