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Re: Policy regarding virtual packages



On Monday 28 August 2006 18:09, Jonas Meurer took the opportunity to say:
> On 28/08/2006 Magnus Holmgren wrote:
> > Making mail-transport-agent the empty package, and having it depend only
> > on exim4 (the default), should work. Of course, exim4 can't conflict with
> > it (but it's enough that all the others do), so if the default is changed
> > then the old default, the new default, and the empty package have to be
> > modified, but not the packages depending on mail-transport-agent. I don't
> > think that this is the right solution though. It's just a thought.
>
> this way, no virtual package would exist at all. 

That would appear to be incorrect. The Debian Policy Manual, § 7.4, defines a 
virtual package as "one which appears in the Provides control file field of 
another package". It goes on to say that "If there are both concrete and 
virtual packages of the same name, then the dependency may be satisfied (or 
the conflict caused) by either the concrete package with the name in question 
or any other concrete package which provides the virtual package with the 
name in question." 

> mail-transport-agent 
> would depend on exim4, and every package depending on
> mail-transport-agent would do so as well.
> no alternative mta could be installed together with packages depending
> on mail-transport-agent.

Also incorrect. All alternative mta packages would still Provides: 
mail-transport-agent, which means that any of them could satisfy the 
dependency in place of the (empty) concrete mail-transport-agent package.

-- 
Magnus Holmgren        holmgren@lysator.liu.se
                       (No Cc of list mail needed, thanks)

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