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To resolve dependencies like "pkg:arch" we create a package with the
name "pkg:arch" and the architecture "any". We create these packages
only if a dependency needs it as these kind of dependencies aren't that
common. This commit ensured that in the even this architecture specific
dependency is the only relation this package has we still create the
underlying package to have them available in provides resolution.
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This doesn't allow all tests to run cleanly, but it at least allows to
write tests which could run successfully in such environments.
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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Gbp-Dch: ignore
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Now that we can dynamically create dependencies and provides as needed
rather than requiring to know with which architectures we will deal
before running we can allow the listparser to parse all records rather
than skipping records of "unknown" architectures.
This can e.g. happen if a user has foreign architecture packages in his
status file without dpkg knowing about this architecture (or apt
configured in this way).
A sideeffect is that now arch:all packages are (correctly) recorded as
available from any Packages file, not just from the native one – which
has its downsides for the resolver as mixed-arch source packages can
appear in different architectures at different times, but that is the
problem of the resolver and dealing with it in the parser is at best a
hack (and also depends on a helpful repository).
Another sideeffect is that his allows :none packages to appear in
Packages files again as we don't do any kind of checks now, but given
that they aren't really supported (anymore) by anyone we can live with
that.
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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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- negative dependencies need to apply to all architectures,
but those with a specific architecture only apply to this one
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