Bug#1029586: apt: "apt-cache rdepends --installed" false positives

[Vincent Lefevre <vincent@vinc17.net>]

On 2023-01-25 10:45:53 +0100, Julian Andres Klode wrote:
> You want to use `apt list '?any-version(?installed?depends(?exact-name(libpcre3)))'`
> instead (with apt >= 2.5.4). In earlier versions you may use:
> apt list '?any-version(?archive(now)?depends(?exact-name(libpcre3)))'

Note that this is not documented. The apt(8) man page just says

  list
    list is somewhat similar to dpkg-query --list in that it can
    display a list of packages satisfying certain criteria. It supports
    glob(7) patterns for matching package names as well as options to
    list installed (--installed), upgradeable (--upgradeable) or all
    available (--all-versions) versions.

but the glob(7) man page is just about globbing pathnames. And
the dpkg-query(1) man page doesn't mention anything about the
above syntax (in case it would be accepted).

> The behavior of patterns is better defined than that of the legacy
> (r)depends tools. The behavior of rdepends here is not necessarily
> useful, but it is the way it is. These commands are provided as-is
> and will not receive drastic changes in behavior.
> 
> The --installed flag here behaves exactly as it is documented.

The documentation in apt-cache(8) is confusing, because "package"
could either refer to a package name or to a particular version.
However, the dependency relation makes sense only with a particular
version.

And the (r)depends entries in apt-cache(8) should suggest to use
patterns instead. Moreover, it should be clear for the user how to
find the documentation.

> It filters the output list by packages that are installed; it
> doesn't say anything about restricting matching to installed
> versions only - matching always happens on all versions effectively.
> 
> The same behavior you can get with patterns by using
> 
> `apt list '?installed?depends(?exact-name(libpcre3))'`
> 
> For a machine readable output, pass the pattern to apt-cache show.

Apparently with the "?any-version" as mentioned above, otherwise the
output is incorrect (and is even more confusing, because for instance,
bti 034-6+b1 is output while this is actually only the older version
bti 034-5+b1 that depends on libpcre3). But this is not documented in
the man pages ("man -K any-version" finds no man pages).

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Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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