Re: [gentoo-dev] Multislot dependencies

[Bernd Steinhauser]

Tiziano Müller schrieb:
> Hi everyone
>
> I'd like to bring bug #229521 to your attention and see whether we can
> come up with a solution for it.
>
> The problem:
> A package "foo" depends on a slotted package "bar" _and_ more than one
> slot of "bar" can satisfy this dependency.
>
> Why this is a problem:
> If the dependency looks like one of the following:
> * DEPEND=">=cat/bar-2"
> * DEPEND="<=cat/bar-3"
> * DEPEND="|| ( cat/bar:2 cat/bar:3 )
> then the package manager doesn't know after building "foo" which slot of
> "bar" has been used to build "foo". On the other hand might this
> information be needed to debug problems with package "foo".
>
> The problem gets even worse as soon as RDEPEND comes in:
> (assuming the same examples from above but with RDEPEND)
> * The package manager currently doesn't record which slot has been used
> and can't therefore track whether the user will destroy something in
> case he uninstalls one of the slots of "bar"
> * The package manager can't sanely consider whether an update for a slot
> is actually needed

There is a section in PMS, that tries to address this.

=================
Slot Dependencies
A named slot dependency consists of a colon followed by a slot name. A 
specification with
a named slot dependency matches only if the slot of the matched package 
is equal to the slot
specified. If the slot of the package to match cannot be determined 
(e.g. because it is not a
supported EAPI), the match is treated as unsuccessful.
An operator slot dependency consists of a colon followed by one of the 
following operators:
* Indicates that any slot value is acceptable. In addition, for runtime 
dependencies, indicates
that the package will not break if the matched package is uninstalled 
and replaced by a
different matching package in a different slot.
= Indicates that any slot value is acceptable. In addition, for runtime 
dependencies, indicates
that the package will break unless a matching package with slot equal to 
the slot of the
best installed version at the time the package was installed is available.
To implement the equals slot operator, the package manager will need to 
store the slot of the
best installed version of the matching package. The package manager may 
do this by appending
the appropriate slot after the equals sign when saving the package’s 
dependencies. This syntax
is only for package manager use and must not be used by ebuilds.
=================

So, if you go with that, the dependency would look like this:
DEPEND=">=cat/bar-2:="

That means, that it accepts any slot of versions above version 2, but 
restricts it to the slot it has been built against, at runtime.
The combination of >= and := might look a bit ugly, so maybe it might 
indeed be useful to specify a way to provide a list of slots.
But it would work in most cases.

Regards,
Bernd

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