{ config, pkgs, lib, haskellLib, buildModules, ... }:
let
  builder = haskellLib.weakCallPackage pkgs ../builder {
    inherit haskellLib;
    ghc = config.ghc.package;
    inherit (config) nonReinstallablePkgs hsPkgs;
  };

in

{
  # this has a slightly modified option type. we will *overwrite* any previous
  # setting of nonRelocatablePkgs, instead of merging them.  Otherwise you
  # have no chance of removing packages retroacively.  We might improvie this
  # by implementing a logic that would allow +xxx to be added, -xxx to be removed
  # and if it's not a list of -/+ prefixed strings, be assumed to be overwriting.
  # This seems ugly.
  options.nonReinstallablePkgs = lib.mkOption {
    type = (lib.types.listOf lib.types.str) // {
      merge = loc: defs: lib.last (lib.getValues defs);
    };
  };

  options.reinstallableLibGhc = lib.mkOption {
    type = lib.types.bool;
    default = false;
    description = "Is lib:ghc reinstallable?";
  };

  # Dependencies (with reinstallable-lib:ghc)
  #
  #              .--------.           .------------------.
  #              | pretty | < ------- | template-haskell |
  #              '--------'           '------------------'
  #                   v                          |
  #              .---------.     .-------.       |
  #              | deepseq | - > | array |       |
  #              '---------'     '-------'       v
  #                    v            v         .-------------.
  # .----------.  .----------.  .------.   .- | ghc-boot-th |
  # | ghc-heap |  | ghc-prim |  | base |< -'  '-------------'
  # '----------'  '----------'  '------'  .----------------.
  #       |          v           |  |     | integer-simple |
  #       |       .-----.        |  '-- > |-------or-------|
  #       '---- > | rts | < -----'        | integer-gmp    |
  #               '-----'                 '----------------'
  #
  # without reinstallable-lib:ghc, this is significantly larger.

  config.nonReinstallablePkgs =
    [ "rts" "ghc-heap" "ghc-prim" "integer-gmp" "integer-simple" "base"
      "deepseq" "array" "ghc-boot-th" "pretty" "template-haskell"
      # ghcjs custom packages
      "ghcjs-prim" "ghcjs-th"
    ]
    ++ lib.optionals (!config.reinstallableLibGhc) [
      "ghc-boot"
      "ghc" "Cabal" "Win32" "array" "binary" "bytestring" "containers"
      "directory" "filepath" "ghc-boot" "ghc-compact" "ghc-prim"
      # "ghci" "haskeline"
      "hpc"
      "mtl" "parsec" "process" "text" "time" "transformers"
      "unix" "xhtml"
      # "stm" "terminfo"
    ];

  options.bootPkgs = lib.mkOption {
    type = lib.types.listOf lib.types.str;
  };

  config.bootPkgs =  [
     "rts" "ghc-boot-th"
     "ghc-heap" # since ghc 8.6.
  ]
    ++ lib.optional (!config.reinstallableLibGhc) "ghc";

  options.hsPkgs = lib.mkOption {
    type = lib.types.unspecified;
  };

  config.hsPkgs =
    { inherit (builder) shellFor ghcWithPackages ghcWithHoogle;
      buildPackages = buildModules.config.hsPkgs;
    } //
    lib.mapAttrs
      (name: pkg: if pkg == null then null else builder.build-package pkg)
      (config.packages // lib.genAttrs (config.nonReinstallablePkgs ++ config.bootPkgs) (_: null));
}