cabal sdist does not call the sdist build hook in custom Setup.hs

[duncan]

The cabal sdist command only runs the default actions, it does not call the sdist hook that gets called if you runghc Setup sdist.

The problem is there is no external method for invoking the sdist hook. Calling ./setup sdist performs the whole action, but we only want to prepare the tree and not tar it up, since cabal sdist uses internal tar code rather than calling an external tar program (which typically does not exist on windows).

[duncan]

See #372.

What we need is for the command line interface to support generating a tarball image in a given location. That way an external tool like cabal-install can call it and then call tar itself.