Bug#759260: removal of the Extra priority.

[Jonathan Nieder <jrnieder@gmail.com>]

Santiago Vila wrote:

> In this case, however, I fail to see the rationale for actually
> *dropping* the extra priority, other than "it's not useful for me".
> Well, it may be useless for you but it's still useful for me.

I have found the 'extra' priority to be useful personally, too.
Enough so that when that information has been incorrect (e.g., library
that is actually important being marked as 'extra'), I've been
motivated enough to file bugs with patches to fix it.  And received
pushback from maintainers that don't understand what the field is for,
are confused about having to maintain it in two places (debian/control
and the ftpmasters override file), and are not especially happy with
having to take patches fixing it.

I am fond of the feature:

 * it makes it easier as a sysadmin to know what packages are in some
   sense the "default" version among several alternatives, and allows
   a sysadmin in a multiuser system to know what packages are safe
   to install without having to deal with conflicts (as you discussed)

 * it makes it easier as a packager to notice when a new dependency
   might create conflicts with other packages --- even when those
   conflicts are introduced after the dependency is added

But I don't get those benefits if people are not setting the Priority
field correctly.  As long as there is not will in the project to
maintain the field, it is tempting to avoid confusion by no longer
providing it (which is why I like the patch from this bug).

Alternatively, if we want to keep it, there are some missing tools
that could make life easier and would make the decision to keep the
extra priority easier:

 - self-service modification to (at least one's own packages in) the
   overrides file

 - when the overrides file currently matches a package's priority,
   automatically propagating over new changes from the package

 - detecting (e.g., at lint time, upload time, or on the PTS) when a
   priority change or new dependency is going to involve priority
   changes for other packages

 - auto-generating a patch to make the package match overrides

My two cents,
Jonathan