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Git-Dch: Ignore
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How the Multi-Arch field and pkg:<arch> dependencies interact was
discussed at DebConf15 in the "MultiArch BoF". dpkg and apt (among other
tools like dose) had a different interpretation in certain scenarios
which we resolved by agreeing on dpkg view – and this commit realizes
this agreement in code.
As was the case so far libapt sticks to the idea of trying to hide
MultiArch as much as possible from individual frontends and instead
translates it to good old SingleArch. There are certainly situations
which can be improved in frontends if they know that MultiArch is upon
them, but these are improvements – not necessary changes needed
to unbreak a frontend.
The implementation idea is simple: If we parse a dependency on foo:amd64
the dependency is formed on a package 'foo:amd64' of arch 'any'. This
package is provided by package 'foo' of arch 'amd64', but not by 'foo'
of arch 'i386'. Both of those foo packages provide each other through
(assuming foo is M-A:foreign) to allow a dependency on 'foo' to be
satisfied by either foo of amd64 or i386. Packages can also declare to
provide 'foo:amd64' which is translated to providing 'foo:amd64:any' as
well.
This indirection over provides was chosen as the alternative would be to
teach dependency resolvers how to deal with architecture specific
dependencies – which violates the design idea of avoiding resolver
changes, especially as architecture-specific dependencies are a
cornercase with quite a few subtil rules. Handling it all over versioned
provides as we already did for M-A in general seems much simpler as it
just works for them.
This switch to :any has actually a "surprising" benefit as well: Even
frontends showing a package name via .Name() [which doesn't show the
architecture] will display the "architecture" for dependencies in which
it was explicitely requested, while we will not show the 'strange' :any
arch in FullName(true) [= pretty-print] either. Before you had to
specialcase these and by default you wouldn't get these details shown.
The only identifiable disadvantage is that this complicates error
reporting and handling. apt-get's ShowBroken has existing problems with
virtual packages [it just shows the name without any reason], so that
has to be worked on eventually. The other case is that detecting if a
package is completely unknown or if it was at least referenced somewhere
needs to acount for this "split" – not that it makes a practical
difference which error is shown… but its one of the improvements
possible.
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We parse all architectures we encounter recently, which means we also
parse packages from architectures which are neither native nor foreign,
but still came onto the system somehow (usually via heavy force).
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Gbp-Dch: ignore
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Expecting the worst is easy to code, but has its disadvantages e.g.
by creating package structures which otherwise would have never
existed. By creating the provides instead at the time a package
structure is added we are well prepared for the introduction of partial
architectures, massive amounts of M-A:foreign (and :allowed) and co as
far as provides are concerned at least. We have something relatively
similar for dependencies already.
Many tests are added for both M-A states and the code cleaned to
properly support implicit provides for foreign architectures and
architectures we 'just' happen to parse.
Git-Dch: Ignore
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Conflicts:
apt-pkg/acquire-item.cc
cmdline/apt-key.in
methods/https.cc
test/integration/test-apt-key
test/integration/test-multiarch-foreign
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On single-arch the parsing was creating groupnames like 'apt:amd64' even
through it should be 'apt' and a package in it belonging to architecture
amd64. The result for foreign architectures was as expected: The
dependency isn't satisfiable, but for native architecture it means the
wrong package (ala apt:amd64:amd64) is linked so this is also not
satisfiable, which is very much not expected.
No longer excluding single-arch from this codepath allows the generation
of the correct links, which still link to non-exisiting packages for
foreign dependencies, but natives link to the expected native package
just as if no architecture was given.
For negative arch-specific dependencies ala Conflicts this matter was
worse as apt will believe there isn't a Conflict to resolve, tricking it
into calculating a solution dpkg will refuse.
Architecture specific positive dependencies are rare in jessie – the
only one in amd64 main is foreign –, negative dependencies do not even
exist. Neither class has a native specimen, so no package in jessie is
effected by this bug, but it might be interesting for stretch upgrades.
This also means the regression potential is very low.
Closes: 777760
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We use test{success,failure} now all over the place in the framework, so
its only consequencial to do this in the situations in which we test for
a specific output as well.
Git-Dch: Ignore
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- ignore foreign architectures if we check if a provides has only one
resolver as it's basically the same for the user, so no need to choose
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- prefer native providers over foreigns even if the chain is foreign
The code preferred real over virtual packages and based on priorities.
This is changed in so far that a real package from any arch is preferred
over any virtual provider and if priorities doesn't help in choosing the
best provider we choose it based on architectures
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