ZuriHac 2017

This is a page to collect ideas for Cabal/Hackage hacking tasks/mini-projects for ZuriHac 2017. It is an updated version of a similar page for the 2016 HaskellX 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.

Easy tickets suitable for beginners

See https://github.com/haskell/cabal/issues?q=is%3Aopen+is%3Aissue+label%3A%22meta%3A+easy%22 and https://github.com/haskell/cabal/issues?q=is%3Aopen+is%3Aissue+label%3Anewcomer for a list of issues tagged "easy" and "newcomer". New contributors to cabal-install/Cabal code base should be able to find something to cut their teeth on in those lists.

Strategically important projects

Mostly Cabal 2.0/3.0 and related. 2.0 is the next release due Real Soon Now that will have hackage-security enabled by default and an updated preview version of new-build feature (see below). 3.0 is the more distant future version in which new-build will replace old build commands and sandboxes.

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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.

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• Improve cabal new-build

  new-build is a major reworking of how Cabal/cabal-install works internally that unifies old build commands and sandboxes and is the main focus of our efforts right now. 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 a more detailed explanation.

  There is a lot of work still to be done on new-build, and most of it can be done in parallel and in groups. We compiled the following list of tasks (roughly sorted by difficulty) that we feel are offering the most pay off right now and are suitable in scope for the hackathon:

  • 'cabal new-install' for binaries. No relevant ticket, but should basically work just like cabal install foo does today for binaries modulo using the store for library dependencies. Should be easy to implement (new-build foo + Setup.hs copy).
  • Integration tests for new-build (e.g.: new-build everything on Stackage) https://github.com/haskell/cabal/issues/3322
  • Fix this annoying bug: ghc-options applies to all dependencies, not just local packages, https://github.com/haskell/cabal/issues/3883
  • 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
  • Go through the remaining issues in https://github.com/haskell/cabal/issues/3104 (difficulty: moderate)
  • Get the new-clean PR into shape.
  • Allow "sandbox without project file" functionality in new Cabal. https://github.com/haskell/cabal/issues/3730 (related to GHC environments, see extra-packages feature).
  • Go through the issues in the Galois meta tracking ticket: https://github.com/haskell/cabal/issues/3577
  • Build on top of the cabal new-build code to support cabal {run,test,bench} etc. Relevant ticket: https://github.com/haskell/cabal/issues/3638
  • Improve cabal new-haddock.
  • Add support for git/darcs/... dependencies, https://github.com/haskell/cabal/issues/2189 (makes sense to start with tarball dependencies before tackling SCM ones -- tarballs are easier to test)

If the above is not enough, you can pick a task from the 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).

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Not critically important, but good to have

• 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. The new user guide TOC should look like roughly 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.

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• 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.

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• Improvements in the release process.

  This is mainly about automating the process of producing binaries for various platforms (Linux i386/x86-64, OS X, Windows x32/x64). We can either use Travis and AppVeyor or the haskell.org infrastructure. The latter requires extending the code of GHC Builder to support arbitrary Haskell projects besides just GHC, because that's what they (haskell.org) want to use for their build farm. Talk with Gershom (@gbaz/@sclv) if he's online about haskell.org integration.

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

  Builds on the new Parsec parser work (see #2865). This should make it possible to programmatically edit .cabal files while preserving comments and formatting.

  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.