#+TITLE: The Future of Haskell Packaging in Nix

* DONE Use Function Application To Escape Override Hell
* DONE Guarantee Consistent Builds and Obsolete =overrideScope=
* DONE Map Cabal Files To Nix Without Information Loss
* TODO Implement Proper Dependency Resolution
* TODO Develop Intelligent Policies for Post-processing and Patching
* TODO Users Need a Configuration Mechanism That Is Both Simpler and More Powerful
* TODO Deal With Infinite Recursions in Test Dependencies
* DONE Set up a Sufficiently Powerful Build Farm
* TODO Define and Publish Processes for Managing the Package Set(s)
* DONE Publish All of Hackage

  We publish 10,745 package versions out of 60,504 available ones, i.e. 18% of
  Hackage. Those packages are selected as follows: we distribute the latest
  version of every package --- 8,764 builds --- plus an additional 1,981 older
  versions that are required by the various LTS Haskell and Stackage Nightly
  package sets we support.

* TODO Generate Differential Build Expressions
* TODO Generate Build Expressions for Hydra
* TODO Add Support for Mega Repositories to =cabal2nix=
* TODO Support Building With =stack=
* TODO Support multi-output derivations

  Put static, shared, and profiled library variants into separate output so
  that we can build everything without forcing users to download all that stuff
  if they just want the regular build.
* TODO Write a =ghcWithPackages= combinator to create conglomerate workspaces

  Thomas Strobel <thomas@strobel.eu> suggested this:

  I want to hack on a set of libraries, say transformers and mtl, and I'd like
  to do that in an environment that contains criterion, QuickCheck, etc. So I
  run

    stackWithPackages (hp: {
      sources = with hp; [transformers mtl];
      env = with hp; [criterion QuickCheck];
    })

  This should create a conglomerate workspace / nix-shell environment that
  contains the source code for transformers and lens in subdirectories plus a
  stack.yaml file that builds them both:

    stack.yaml
    mtl / ...
    transformers ...

  The environment would contain a GHC with criterion and QuickCheck registered
  in appropriate LTS versions so that the stack builds don't compile anything
  except the packages I'm hacking on.

  The value of env could possibly be auto-determined from the dependencies of
  transformers and mtl.
* TODO Solve the too-eager evaluation of meta.broken

  We'd like to mark builds that are known to fail with `meta.broken = true`,
  but this is impractical because users have no way to override that setting if
  they discover that the package has been fixed in a new version.