Bug#945269: debian-policy: packages should use tmpfiles.d(5) to create directories below /var

[Simon McVittie <smcv@debian.org>]

On Mon, 05 Jun 2023 at 01:36:25 +0100, Luca Boccassi wrote:
> If it is useful, adding a "default-tmpfiles" or so virtual package
> would be fine by me - but with the kfreebsd port being retired soon,
> and i386 (for hurd) going the way of the dodo, I'm not sure it would
> be very useful? I don't think it would be a problem to add it, if it
> turns out to be of use though.

What this would look like, in src:systemd:

    Package: systemd
    Provides: default-systemd-tmpfiles, systemd-tmpfiles

    Package: systemd-standalone-tmpfiles
    Provides: systemd-tmpfiles

(or maybe the other way round, depending what conclusion we come to on
the choice between (1.) and (2.)), and then in dependent packages:

    Package: foo-service
    Depends: default-systemd-tmpfiles | systemd-tmpfiles

The benefits of that over having foo-service depend directly on
"systemd | systemd-tmpfiles" or
"systemd-standalone-tmpfiles | systemd-tmpfiles" are fairly minor, but the
cost is also fairly minor; and if we want this, we should set it up
*before* lots of packages start adding a dependency on the -tmpfiles or
-sysusers interfaces. The benefits I see are:

- if we find out that the dependency we first added is a practical problem
  for whatever reason, we can swap the default with a src:systemd upload,
  without needing multiple maintainers to touch all the dependent packages;

- if we get a useful non-Linux port (admittedly this looks increasingly
  unlikely) which cannot compile src:systemd, then their reimplementation
  of these interfaces can have Provides: default-systemd-tmpfiles on that
  architecture, without affecting Linux architectures
  (the same way dbus-x11 Provides default-dbus-session-bus on non-Linux
  ports, even though it's dbus-user-session that Provides the virtual
  package on Linux)

    smcv