add a --with-package-conf= flag to configure

[duncan]

From  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=317803

Consider adding a --with-package-conf= flag to the configure command,
or the register command.

There is partial support for this internally in Cabal, though only for GHC of course. We have to decide if and how we want to present this feature given that it is currently GHC-only. Could it be done in a way that allows other implementations to provide a similar feature in future without us having to change the Cabal user interface?

[duncan]

Sun Jan 13 23:25:36 GMT 2008  Duncan Coutts <duncan@haskell.org>
  * Add configure --package-db= flag to use specific package db
  Should allow satisfying deps from the given package db and should register
  into that db. It is not thoroughly tested however.

See also:  http://www.haskell.org/pipermail/cabal-devel/2008-January/001927.html

It still needs proper testing and documenting in the user guide. Marking this remaining task as easy.

We should also consider if the --user and --global flags to the install and register commands still make sense with the slight change in semantics of those flags in the configure step.

[duncan]

Replying to duncan:

It still needs proper testing and documenting in the user guide. Marking this remaining task as easy.

Now documented and people have been using it and it seems to work ok.

We should also consider if the --user and --global flags to the install and register commands still make sense with the slight change in semantics of those flags in the configure step.

I'm not at all convinced that these flags make sense. I think changing the package db to register into after building is a very unsafe thing to do. There is no guarantee that the dependent packages exist or that if they do that they are ABI compatible with the ones that we built against. I think we should deprecate the feature. If people want to do it anyway we provide a way to generate the package registration file already.