Hackathon 2016

This is a page to collect ideas for Cabal/Hackage hacking tasks/mini-projects for the Haskell eXchange Hackathon 2016. It is an updated version of a similar page for the 2015 infrastructure hackathon.

Please use the #hackage IRC channel on freenode for online discussions.

Feel free to expand individual bullet points into full (linked) pages or tickets/issues.

Strategically important projects

Mostly Cabal 2.0 and related.

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• Package collections in cabal-install and hackage-server

  The idea here is to support package collections directly in our infrastructure. Currently package collections like Stackage are implemented indirectly by specially crafted cabal.config/cabal.project.freeze files. Collections are also to be distributed via hackage, allowing anyone to define and distribute collections.

  A specification was posted to the libraries list recently. There is also some prototype code available for cabal-install. The cabal-install code adds solver support and allows for set-like operations on collections. Nothing has been started yet for hackage-server.

  This is an important feature since package collections are one of the two big solutions to cabal hell. This is not a huge project. There's probably enough for two people to work on the client side and two on the server side.

Link to https://github.com/haskell/cabal/issues?q=is%3Aopen+is%3Aissue+label%3A%22meta%3A+easy%22

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• Improve cabal new-build

  See Edward's blog post: http://blog.ezyang.com/2016/05/announcing-cabal-new-build-nix-style-local-builds/. for an intro to new-build and explanation why it's important.

  This is not a neat self-contained project. There are lots of parts to this project and it will require people to work together.

  List of all open new-build issues: https://github.com/haskell/cabal/issues?q=is%3Aissue+is%3Aopen+label%3A%22cabal-install%3A+nix-local-build%22

  • Get the new-clean PR into shape.
  • Building on top of the cabal new-build code to support cabal {run,test,bench} etc.
  • cabal new-haddock
  • Go throuth the issues in the Galois meta tracking ticket: https://github.com/haskell/cabal/issues/3577
  • UX design for user-wide environments ('cabal new-install'), relevant ticket: https://github.com/haskell/cabal/issues/3737
  • UX design for 'cabal new-update' (index freezing by default, interaction with cabal.project.freeze, talk with @ezyang and/or @hvr if they're online), relevant ticket: https://github.com/haskell/cabal/issues/3832
  • 'cabal new-install' for binaries. No relevant ticket, but
  • Test Duncan's ghc-environments PR (use GHC 8.0.2 snapshot). PR link: https://github.com/haskell/cabal/pull/3936
  • ghc-options applies to all dependencies, not just local packages, https://github.com/haskell/cabal/issues/3883
  • Locking the store for concurrent builds: https://github.com/haskell/cabal/issues/3741
  • Allow "sandbox without project file" functionality in new Cabal. https://github.com/haskell/cabal/issues/3730 (related to GHC environments, see extra-packages feature)
  • Replace new-build's call to sdist with new command which lists sources of things that will be built, https://github.com/haskell/cabal/issues/3401 (deprecate sdist hooks, use stack code as reference, but use Cabal's file globs)
  • Integration tests for new-build (e.g.: new-build everything on Stackage) https://github.com/haskell/cabal/issues/3322
  • Go through the remaining issues in https://github.com/haskell/cabal/issues/3104 (difficulty: moderate)
  • Add support for git/darcs/... dependencies, https://github.com/haskell/cabal/issues/2189 (makes sense to start with tarballs)

• Cabal documentation.

  Cabal's user guide got quite a bit better recently, but there's still a lot of room for improvement. In particular, we want to put more emphasis on the cabal-install tool at the expense of the Setup.hs interface and add a tutorial section. Ideally, the user guide would look like approximately this:

  1. Intro
  2. Tutorial, p.1 - how to use cabal-install to build and install existing packages
  3. Tutorial, p.2 - how to develop programs using cabal-install and write .cabal files -- basically, an updated version of https://wiki.haskell.org/How_to_write_a_Haskell_program.
  4. .cabal format reference
  5. cabal-install command reference
  6. cabal new-build chapter
  7. Appendix: Cabal spec (i.e., the Setup.hs interface)

  Anyone considering this should feel empowered to make decisions. You could decide to start from scratch with a new structure and just pinch material from the existing docs. You might want to fully split into tutorial and reference.

• A new website for cabal-install/Cabal.

  Our website hasn't been updated in ages, so a facelift is long due. It doesn't have to be super-advanced, a simple Hakyll-based static page with a blog/news feed would suffice. Start by looking at the https://github.com/haskell/cabal-website repo.

• Improvements in the release process.

  This is mainly about

• Rewrite of the .cabal file parser. #2865

  @phadej (Oleg Grenrus) is the person to talk to about this issue. Help him with merging, experiment with using the new parser instead of the old one, write tests.

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• New AST for .cabal files (not an easy one!).

  Builds on the new parser.

  See http://code.haskell.org/~duncan/cabal-ast-experiment/

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• Include-able Common Stanzas #2832

  Builds on the new parser+AST. Allow to reduce duplication by moving common definitions to include-able common stanzas which can then be included from other stanzas.