Re: [gentoo-user] "Multiple package instances ....". Help me understand this emerge error, please.

[Alan McKinnon]

On 22/02/2014 23:15, Alan Mackenzie wrote:
> Hi, Gentoo.
>
> I've just tried an emerge -puND world, after a shockingly long interval.
> I got the error message:
>
>    !!! Multiple package instances within a single package slot have been pulled
>    !!! into the dependency graph, resulting in a slot conflict:
>
> , etc.
>
> To simplify the problem, I tried to emerge an individual package
> identified in that message, and tried emerge -p libpng.  I got the same
> message, with this:
>
> ###############################################################################
> !!! Multiple package instances within a single package slot have been pulled
> !!! into the dependency graph, resulting in a slot conflict:
>
> media-libs/libpng:0
>
>   (media-libs/libpng-1.5.17-r1::gentoo, installed) pulled in by
>     media-libs/libpng:0/0= required by (x11-libs/cairo-1.12.14-r4::gentoo, installed)
>     >=media-libs/libpng-1.4:0/0= required by (app-editors/emacs-24.3-r2::gentoo, installed)
>     media-libs/libpng:0/0= required by (media-libs/libwebp-0.3.1::gentoo, installed)
>     media-libs/libpng:0/0= required by (net-print/cups-filters-1.0.36-r1::gentoo, installed)
>     media-libs/libpng:0/0= required by (kde-base/kdelibs-4.11.2-r1::gentoo, installed)
>     media-libs/libpng:0/0= required by (dev-qt/qtgui-4.8.5-r1::gentoo, installed)
>     media-libs/libpng:0/0= required by (app-text/poppler-0.24.3::gentoo, installed)
>     (and 3 more with the same problems)
>
>   (media-libs/libpng-1.6.8::gentoo, ebuild scheduled for merge) pulled in by
>     (no parents that aren't satisfied by other packages in this slot)
> ###############################################################################
> Clearly, I'm trying to update libpng-1.5.17 to libpng-1.6.8.  What does
> this portion of the message mean:
>
>     media-libs/libpng:0/0=
>                      ^^^^^
>
> ?  Is it somehow telling me that cairo and friends require the currently
> installed version, whatever that is?  Where is this format documented?  I
> couldn't find anything about it in the Gentoo handbook, and not in the
> emerge man page either.
>
> What do I have to do to get this thing emerged?
>
> Thanks!
>

You've hit the dreaded sub-slot (a new portage feature). It causes no
end of trouble as so few people know how it really works, but it's
intended to replace @preserved-rebuild by DoingItRite and finally make
revdep-rebuild obsolete.

It's documented in man 5 ebuild under these headings:

Atom Slots
Sub Slots
Atom Slot Operators
SLOT

libpng:0/0 is libpng SLOT 0 which has been around since EAPI1 and
SUBSLOT 0 which is new.

Take cairo which is one of your deps. In the ebuild:

RDEPEND="
        media-libs/libpng:0=
"

eix libpng shows:

     (0)    1.5.15 1.5.17-r1 (~)1.6.6(0/16) (~)1.6.7(0/16) 1.6.8(0/16)
(~)1.6.9(0/16)

That shows libpng-1.5.* have slot/subslot 0/0 and
           libpng-1.6.* have slot/subslot 0/16
where presumably "16" is shorthand for "1.6" in the version



Now read those headings in the man page, you will find this gem:

"=      Indicates  that any slot value is acceptable. In addition, for
runtime dependencies, indicates that the package will break unless a
matching package with slot and  sub-slot  equal to  the  slot  and
sub-slot  of  the  best  installed version at the time the package was
installed is available.

                     Examples:
                          dev-libs/icu:=
                          dev-lang/perl:=
                          dev-libs/glib:=
"

in other words, even though libpng-1.5.17-r1 and libpng-1.6.8 are in the
same SLOT, nevertheless cairo will break if you upgrade libpng that way.

Or expressed another way in language from before sub-slots, cairo will
stop working properly after the emerge world until you run
revdep-rebuild and fix and the borkage


The world update wants to upgrade libpng as a new stable version is
available but portage won't do it as it will break packages that use libpng.


All my hosts here are up to date so I can't reproduce your problem:

- is portage up to date runnign latest version in your tree? Update that
first (always a good idea anyway)
- are you sure that's an emerge failure and not just a convoluted info
message? Perhaps post the entire emerge output.


-- 
Alan McKinnon
alan.mckinnon@×××××.com