Nix expression for generating a build of keystone that won't try writing to node_modules in /nix/store

generate.sh

#!/bin/sh -eu

# You need nix installed to run this:
# https://nixos.org/nix/download.html

export NIX_PATH="nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/d0d905668c010b65795b57afdf7f0360aac6245b.tar.gz"

rm -f default.nix node-env.nix node-packages.nix package.json

cat <<EOF > package.json
[
  { "keystone": "4.0.0-beta.5" }
]
EOF

cat <<EOF > supplement.json
[
  { "uglify-js": "2.8.29" }
]
EOF

cat <<EOF > default.nix
{ stdenv
, pkgs ? import <nixpkgs> {}
, system ? builtins.currentSystem
, nodejs ? pkgs.nodejs-6_x
}:

let
  nodePackages = import ./composition.nix {
    inherit pkgs system nodejs;
  };
  inherit (nodejs) python;

in nodePackages // {
  "keystone-4.0.0-beta.5" = nodePackages."keystone-4.0.0-beta.5".override {
    # you must do this step so that node_modules is written to before being
    # sealed in /nix/store
    postInstall = ''
     KEYSTONE_PREBUILD_ADMIN=true npm run build
   '';
  };
}
EOF

"$(nix-build '<nixpkgs>' -A nodePackages.node2nix --no-out-link)/bin/node2nix" \
     -6 \
     -i package.json \
     -c composition.nix \
     -e node-env.nix \
     --supplement-input supplement.json

nix-build -E 'with import <nixpkgs> {}; callPackage ./default.nix {}'

# Afterwards you should have the bundles here:
#
# % ls -lha result/lib/node_modules/keystone/admin/bundles/js
# total 1.4M
# dr-xr-xr-x 5 rkm staff  170 Jan  1  1970 .
# dr-xr-xr-x 3 rkm staff  102 Jan  1  1970 ..
# dr-xr-xr-x 3 rkm staff  102 Jan  1  1970 11bbac-App
# -r--r--r-- 1 rkm staff 1.4M Jan  1  1970 11bbac-FieldTypes.js
# dr-xr-xr-x 3 rkm staff  102 Jan  1  1970 11bbac-Signin
#
# Note that you also have to set KEYSTONE_PREBUILD_ADMIN=true when you're
# running your app that has keystone as a dependency.
#
# Now keystone won't attempt to write to node_modules in /nix/store.