Build-Depends: some-virtual-package (not stating any real package)

[Ian Jackson]

acpi 0.09-3 says this:
 Build-Depends: debhelper (>= 4), automaken, autoconf, \
                help2man, dpkg-dev (>= 1.9.0)
(linebreak mine).

automaken is only a virtual package.  My recollection was that this
was discouraged by Debian policy, and that instead a real package
should be offered as an earlier alternative.  However, the current
version of Debian policy s7.4 says this:
  If you want to specify which of a set of real packages should be the
  default to satisfy a particular dependency on a virtual package, you
  should list the real package as an alternative before the virtual
  one.

This does not clearly imply the requirement that I and mvo thought
existed.  acpi builds fine with sbuild (obviously) but both apt-get
build-dep and the machinery used by autopkgtest fail.

Is the policy inadequate ?  If so then policy should be fixed in
Debian and acpi needs a fix too.

If policy is correct then gdebi (used by autopkgtest) and
apt-get build-dep need to be fixed to permit this case.

Another possible interpretation is that `in Ubuntu we always want the
Build-Depends to specify which real package to use, so that builds are
predictable'.

Ian.