Haskell + Nix testing

foo.nix

# shell.nix
let
  releaseDrv = import ./release.nix;
  cabal = releaseDrv.haskellPackages.cabal;
in

releaseDrv
  .haskell-nix-sandbox
  .env
  .overrideAttrs (drv: {
    buildTools =
      (drv.buildInputs or []) ++ [ cabal ];
  })

# release.nix
let config = { allowUnfree = true; };
    overlays = [
      (newPkgs: oldPkgs: {
        haskellPackages = oldPkgs.haskellPackages.override { overrides =
          haskellPackagesNew: haskellPackagesOld: {
            # List packages here!
            haskell-nix-sandbox =
              haskellPackagesNew.callPackage ./default.nix {};
          };
        };
      })
    ];
    nixpkgs = <nixpkgs>; # import ./nix/17_09.nix
    pkgs = import nixpkgs { inherit config overlays; };
in
{ inherit (pkgs) haskellPackages;
  inherit (pkgs.haskellPackages) haskell-nix-sandbox;
}

# default.nix
{ callCabal2nix
  ? (import <nixpkgs> {}).haskellPackages.callCabal2nix
}:

callCabal2nix "haskell-nix-sandbox" ./. {}

# haskell-nix-sandbox.cabal
name:                haskell-nix-sandbox
version:             0.0.1
synopsis:            Sandbox for developing haskell on top of nix
homepage:            https://github.com/Steell/haskell-nix-sandbox#readme
Bug-Reports:         https://github.com/Steell/haskell-nix-sandbox/issues
license:             Apache-2.0
license-file:        LICENSE
author:              Steve Elliott
maintainer:          steve@steellworks.com
copyright:           2018 Steve Elliott
category:            Misc
build-type:          Simple

cabal-version:       >=1.10
extra-source-files:
                   LICENSE
                   README.md

library
        ghc-options:    -Wall
        hs-source-dirs: src
        exposed-modules:
                        HaskellNix.Foo

        build-depends:
                      base >= 4.9 && < 5,
                      async >= 2.2.0.0 && < 2.3

executable haskell-nix-sandbox
        hs-source-dirs: exe
        main-is:        Main.hs
        ghc-options:    -threaded -rtsopts -with-rtsopts=-N -Wall
        build-depends:
                      base >= 4.9 && < 5,
                      haskell-nix-sandbox,
                      lens >= 4.0

        default-language: Haskell2010