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authorDavid Kalnischkies <david@kalnischkies.de>2015-09-06 13:32:07 +0200
committerDavid Kalnischkies <david@kalnischkies.de>2015-09-14 15:22:18 +0200
commit3addaba1ff6fe27cc96af5c2d345ee039c2bffec (patch)
treecfbaefb24f12aa82277e41029f07316490cae2b0 /README.make
parent921a962611dfbca7a72b2aa5c499b139dd27ae14 (diff)
implement dpkgs vision of interpreting pkg:<arch> dependencies
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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