Principia and formulas that use software from outside of Ubuntu

[Clint Byrum]

Excerpts from Mark Shuttleworth's message of Tue Jun 14 02:39:10 -0700 2011:
> On 14/06/11 01:47, Clint Byrum wrote:
> > As far as PPA's, they're easy.
> > ensemble add-repository pfa:~kim0/t3h-awesum-formulas kim0
> > ensemble deploy kim0:drupal
> >
> > Having those definitely seems to close the loop and allow people to
> > share and contribute rapidly without waiting on any beuracracy.
> 
> .... but that leaves open the interpretation of dependency resolution.
> Formulas may have dependencies, and it needs to be clear how those
> dependencies will be resolved. Allowing the user to overwrite namespaces
> makes that more... colourful :-)

Thats mitigated if we have the "default" namespaces trusted, allowed to
be deployed when something needs them, but the namespaces that are simply
"known" and not "trusted" wouldn't be considered for automatic resolution
outside of their own namespace. So kim0's drupal can depend on something
that is either in principia, or his own pfa, but not somebody else's pfa
without the user explicitly trusting that other pfa.

This also has the nice effect that deploying something from a PFA/contrib
still resolves its dependencies from the default trusted archives.

Something like this:

/etc/ensemble/namespaces.yaml

ensemble: namespaces
namespaces:
  - principia:
    trusted: true
    archive-url: https://ensemble.ubuntu.com/archive/principia/oneiric
  - contrib:
    trusted: false
    archive-url: https://ensemble.ubuntu.com/archive/contrib/oneiric

And then ~/.ensemble/namespaces.d/pfa-kim0.yaml has

ensemble: namespaces
namespaces:
  - pfa:kim0
    trusted: false
    archive-url: https://launchpad.net/~kim0/pfa/oneiric