{ stdenv, runCommand, writeText, writeScript, writeScriptBin, ruby, lib
, callPackage, defaultGemConfig, fetchurl, fetchgit, buildRubyGem, buildEnv
, linkFarm
, git
, makeWrapper
, bundler
, tree
}@defs:

{ name ? null
, pname ? null
, gemdir ? null
, gemfile ? null
, lockfile ? null
, gemset ? null
, ruby ? defs.ruby
, gemConfig ? defaultGemConfig
, postBuild ? null
, document ? []
, meta ? {}
, groups ? ["default"]
, ignoreCollisions ? false
, ...
}@args:

let
  drvName =
    if name != null then name
    else if pname != null then "${toString pname}-${mainGem.version}"
    else throw "bundlerEnv: either pname or name must be set";

  mainGem =
    if pname == null then null
    else gems."${pname}" or (throw "bundlerEnv: gem ${pname} not found");

  gemfile' =
    if gemfile == null then gemdir + "/Gemfile"
    else gemfile;

  lockfile' =
    if lockfile == null then gemdir + "/Gemfile.lock"
    else lockfile;

  gemset' =
    if gemset == null then gemdir + "/gemset.nix"
    else gemset;

  envPaths = lib.attrValues gems ++ lib.optional (!hasBundler) bundler;

  binPaths = if mainGem != null then [ mainGem ] else envPaths;

  basicEnv = import ./basic args // { inherit drvName pname gemfile lockfile gemset; };

  # Idea here is a mkDerivation that gen-bin-stubs new stubs "as specified" -
  # either specific executables or the bin/ for certain gem(s), but
  # incorporates the basicEnv as a requirement so that its $out is in our path.

  # When stubbing the bins for a gem, we should use the gem expression
  # directly, which means that basicEnv should somehow make it available.

  # Different use cases should use different variations on this file, rather
  # than the expression trying to deduce a use case.

  # The basicEnv should be put into passthru so that e.g. nix-shell can use it.
in
  (linkFarm drvName entries) // {
    passthru = {
      inherit basicEnv;
    };
  }