[pacman-dev] Alternative dependencies.

[Dan McGee]

On Fri, Dec 10, 2010 at 8:58 AM, Xyne <xyne at archlinux.ca> wrote:
> Hi,
>
> Would it be possible to implement support for alternative dependencies, e.g. a
> package that could use either wget or curl to handle downloads?
>
> I know that "provides" can be used to do this, e.g. openjdk6 and jre both
> provide java-runtime to satisfy that dependency in other packages. The approach
> is limited though. Using the example above, we couldn't simply add
> "provides=('download-client')" to both curl and wget because they are not
> interchangeable.
Yes, this is definitely a slightly different problem. To continue your
sentence, "not interchangeable in all cases".

> The basic usage case is when an application is capable of detecting any one of
> a number of different external apps that it can use to satisfy a given
> dependency. There is currently no way to depend on "at least one" of those.
You went abstract here- how many real packages would benefit from this
sort of thing at the moment? What are they?

> I can imagine a very simple syntax for this too, e.g. "depends=('curl ||
> wget')" so the question is whether the dependency-handling mechanism could be
> adapted to check for alternatives. If none are found, it could probably use the
> upcoming "provides" selection dialogue to allow the user to choose the desired
> dependency.
I'm sure we could, and the syntax isn't all that bad.

> So, would that be possible?
> Also, would that be acceptable?
Possible yes. Acceptable- I don't have any serious objections. The
only thing that comes to mind is the likelyhood of abuse as a
replacement for provides, when that is the better facility to express
this.

-Dan