Duncan Coutts
I'm not sure that I do. I think I'd like to see the bigger picture of what you're really trying to achieve.
Honestly, I'm not quite sure what you're trying to do exactly. Perhaps seeing the whole patch would help or if you can explain the use case.
Here's my use case. I've expressed in the form of requirements and how I think they could be solved using ghc and cabal. We have a small team of developers and a much larger team of users who use a very restricted subset of Haskell. We have a version control system. We want everyone to use exactly the same community packages. Currently, we keep these packages under version control and manually modify ghc's package.conf (also under version control). The reason we do this is that the developers and users are able to check out sources to an arbitrary location on their local disk and we want the users to be able to build and run our code without manual configuration or separate installation of anything. Furthermore, each developer and user could have several "workspaces" (checked out versions of the sources at different locations on their local disk) on the go at the same time. We modify ghc's package.conf to use $topdir and relative paths - see http://www.nabble.com/Re%3A-haddock-not-finding-base- lib-docs----%24topdir---p7699303.html - so that package.conf is in sync with the place where the developer / user has checked out their sources (without package.conf needing to be modified on a per user and per workspace basis). The requirement for everyone to use the exactly the same community packages is partly driven by audit requirements. Furthermore, because we are behind a proxy, currently we would have to get every user to modify their registry if we wanted them to install community packages. We'd rather not do that especially as these settings can get over-written e.g. when Internet Explorer gets patched. We'd like to move away from manually modifying ghc's package.conf and to doing things the community way by using cabal more. Here's what I think would work. 1. A developer realises that package A is required. He cabal fetches to a remote-repo-cache which is under version control. This will also fetch any dependencies. 2. He installs package A using the remote-repo-cache and specifying --package- db. Note that the package-db is "[]" in the version control system and only every gets updated in the checked out source. It never gets checked back in. The cabal install of package A updates the package-db. 3. He uses e.g. ghci with -package-conf, -no-user-package-conf and -package A. 4. He checks in the remote-repo-cache. 4. Now another developer wishes to work on the code. 5. He checks out the sources from version control and cabal installs all the packages in the remote-repo-cache specifying --package-db. We'd probably do this in our build system by automatically building any package that has appeared in the repo-cache since the last update. He now has all the packages in the remote-repo-cache and his package.db has been updated to reflect this even though the file itself is not ever checked into the version control system. We'd certainly want this to happen behind the scenes for our users who will not add packages but who will certainly use them (even if they don't realise they are). Dominic.