Bootstrappable Debian - a decision is needed, patches exist
This email is a follow up on the thread started January 2013 . In summary:
it seems that the ability to bootstrap Debian from scratch and the requirement
to extend the Build-Depends syntax meet general agreement.
What is yet to be decided is the concrete format for the Build-Depends syntax extension. The first proposals suggested a syntax which looked like
Build-Depends: foo [amd64] <!stage1>
Which would indicate that the build dependency "foo" would not apply if the
build profile called "stage1" is activated. It was critisized  that this
syntax wastes a meta character and thus prohibits future extensions of the
Build-Depends syntax. Therefore the second proposal (finalised at debconf13)
looked like this:
Build-Depends: foo [amd64] [!profile.stage1]
The rectangular brackets are reused and a prefixed namespace is used to
indicate that "stage1" is a build profile name. We hoped this would be the
final spec, given the previous discussion, but those brackets also got some
pushback  and thus the third version was born:
Build-Depends: foo [amd64] <!profile.stage1>
We wrote down the last two options in form of a spec on the Debian wiki .
Patches for dpkg, python-debian, apt and sbuild implementing the original
format have existed for years . Patches for the new formats have existed for
some time as well . They are surely not perfect but we would like to get
them into a state in which they can be integrated into dpkg. But for that we
need some feedback from the dpkg devs as well as a final decision of the Debian
community about which syntax to choose. We are writing to d-devel this time
because the thread on d-dpkg [6,7] has been dormant for a month once again.
Maybe bringing this issue to a wider audience will help make a decision on this
problem. The results from two years of GSoC [8,9] as well as the year long
efforts of others  cannot bear any fruit without this issue finally being
taken care of.
josch & wookey