stack2nix

stack2.nix

{ pkgs ? import (builtins.fetchTarball https://github.com/nixos/nixpkgs-channels/archive/nixos-unstable.tar.gz) {} }:
let
  yaml = ./stack.yaml;
  cabal2nix = "${pkgs.cabal2nix}/bin/cabal2nix --no-check --no-haddock";
in
pkgs.writeScript "build.sh" ''
  export NIX_PATH=nixpkgs=${pkgs.path}

  resolver=$(awk '/resolver:/{print $2}' ${yaml} | sed 's,\.,_,g')

  echo '{ pkgs ? import (builtins.fetchTarball https://github.com/nixos/nixpkgs-channels/archive/nixos-unstable.tar.gz) {} }:'
  echo '
  let
    inherit (pkgs) lib;
    hs = pkgs.haskell.packages.'$resolver'.override { overrides = a: b: removeAttrs (overrides a b) ["process"]; };

    overrides = self: super: {
  '

  for tuple in $(awk -v OFS='#' '/location:/ {l=1;next} l && /git:/ {git=$2;next} l && /commit:/ {commit=$2;next} git && commit && l { print git, commit; l=0}'< ${yaml}); do
    _IFS=$IFS
    IFS='#'
    set -- $tuple
    IFS=$_IFS
    f=$(mktemp)
    cabal2nix --revision $2 $1 > $f
    name=$(sed -n '/pname/s/pname = "\(.*\)";$/\1/p' $f)
    printf "%s = self.callPackage (%s) {};\n" $name "$(cat $f)"
    rm -f $f
  done

  sed -n '/^extra-deps:/,/^[^-]/s|^- \(\(.*\)-\([0-9.]\+\)$\)|printf "%s = self.callPackage (%s) {};\\n" \2 "$(${cabal2nix} cabal://\1)"|p' ${yaml}  | sh

  echo '};
    this = 
  '
  ${cabal2nix} .
  echo ';
   in pkgs.stdenv.lib.overrideDerivation
      (hs.callPackage this { process = (overrides hs {}).process; })
      (drv: {
        configurePhase =
          # allow mixing process-1.2 and process-1.3
          builtins.replaceStrings ["exit 1"] [": exit 1"] drv.configurePhase;
      })
  '
''

Usage:

$(nix-build stack2.nix) > default.nix
nix-build