Status update on sandboxed builds

[Johan Tibell]

Hi all,

I thought I'd give everyone a status update on the sandboxed build support.

Mikhail has been busy at work implementing automatic rebuilding of
local dependencies. Local dependencies let you can build one
unreleased package against another unreleased package, both residing
in e.g. ~/src. This is similar to cabal-dev's add-source feature, but
instead of installing a snapshot of a local package when the command
is run we create a link to the package and rebuild it when needed.
This means that you will be able to do something like this:

    cd proj
    cabal add-source ~/src/dep
    cabal build  -- builds dep and then proj
    <edit ~/src/dep>
    cabal build  -- builds dep and then proj

This will make it much easier working with collections of libraries.

What remains to be done:

 * Implement the UI described here:
http://hackage.haskell.org/trac/hackage/wiki/PackageEnvironments#Userinterface
. This is mostly done already. We need to merge the current hidden
cabal sandbox-* commands (e.g. cabal sandbox-build) into their
standard variants  (e.g. cabal build).
 * Lots of testing!

Cheers,
Johan