Bug#878905: debian-policy: Document installability recommendations for dependency alternatives

[Simon McVittie <smcv@debian.org>]

On Tue, 17 Oct 2017 at 18:12:29 +0200, Julian Andres Klode wrote:
> (1) dconf-service depends default-dbus-session-bus | dbus-session-bus
> (2) default-dbus-session-bus is provided by an Architecture: all package, but
>     depends on systemd
> 
> APT refuses to install that.

This specific instance of a more general problem is #878878.

> I think it makes sense to amend section 7.1 with the following information:
> 
>     Packages on the left hand side of a pipe symbol should either be installable
>     or should not exist in the given situation (for example, because it is linux-only
>     and the package only exists on non-Linux platform).

In #878878 I'm intending to fix that by:

- changing dbus-user-session from Architecture: all to
  Architecture: linux-any (which means we'll have 20 copies of it instead
  of one, counting non-release architectures, but that's the price we pay
  for retaining best-effort support for non-Linux kernels)

- changing dbus-x11 to add Provides: d-d-s-b [!linux-any]

Is that the resolution that you would recommend?

Thanks,
    smcv