Re: [gentoo-dev] What are || ( ) dependencies?

[Ciaran McCreesh]

On Fri, 17 Dec 2010 20:13:55 -0600
Donnie Berkholz <dberkholz@g.o> wrote:
> > What about if you decide upon a early on, and then later on
> > something hard-depends upon b?
>
> Then you're collapsing the graph too early. =)
> (speaking as an utter novice)

Yeah, but unfortunately, there's no way to figure out when too early
is. What if it's one of a's dependencies that hard-depends upon b?
Until you've decided upon something, you don't know what dependencies
are going to be pulled in, so you're left having to make possibly
incorrect decisions and then try to undo them later on if possible.

> Why is this a problem that needs to be resolved at the specification
> level rather than a difference between implementations? If a package
> manager is making strange choices,

The problem's how you define strange choices. If dependencies aren't
listed best-leftmost, every package manager makes strange choices for
some combinations. Either this can be fixed by getting developers to
always write things best-leftmost, or it can be fixed by mandating
specific behaviour for all package managers for || ( ) deps. I'd much
rather we did the former.

> I'd thought people already knew that this was typical behavior of an
> || group (as per the simple example in ebuild(5)), but you've said
> differently later in this thread. I certainly wouldn't mind
> documenting that left is best in cases where none are installed,
> since this has been expected behavior to those of us who do know.

Well, we're running across a fair number of cases along the lines of
the libX11 one.... https://bugs.gentoo.org/show_bug.cgi?id=348518 is
what prompted the email -- it turns out vlc is by no means the only
package doing this, though, which gives me two options for Paludis: add
in a heuristic that gets that very specific case right (and update PMS
requiring package manglers to do the same), or get people to list their
deps the other way around.

-- 
Ciaran McCreesh