Pass a environment name, node name, and path to a JSON file with a run_list in it, and get back a node that you can call merged_attributes on to get (pretty dang close to) what the node will have as it's attributes during a run. Useful for updating docs to have up-to-date with a pre-commit hook.

load_chef_node.rb

# I'm sure this can all be replaced with a one liner, buried deep in chef somewhere.
# Actually, probably Chef::Client.

require 'json'
require 'chef'
require 'chef/application/solo'
require 'chef/knife/deps'

def setup_node(environment, name, node_config_path)
  Chef::Config[:config_file] = ".chef/knife.rb"
  Chef::Config[:solo] = true


  # load the environment, which gives paths to cookbooks and environments
  env =  Chef::ConfigFetcher.new(Chef::Config[:config_file])
  Chef::Config.from_string(env.read_config, Chef::Config[:config_file])

  # setup some config after loading the config file..
  Chef::Config[:environment] = environment
  Chef::Config[:node_name] = name

  # Loads up all the bookbooks in our path
  cl = Chef::CookbookLoader.new(Chef::Config[:cookbook_path])
  cl.load_cookbooks

  # Create a node -- this also loads up environment config
  node = Chef::Node.build(name)

  # OHAI is needed. It will provide data from your laptop, but we don't
  # show/use the data this provides in any of our attributes
  ohai = ::Ohai::System.new
  ohai.all_plugins
  automatic = ohai.data
  # lies
  automatic['platform_family'] = 'debian'
  # lies, lies
  automatic['lsb'] = {'codename' => 'precise'}
  automatic['memory'] = {'total' => '4096'} # awwyiss fake memory for our one node

  node.automatic_attrs.merge! automatic
  # This loads up the run list from the node file
  node.consume_run_list(JSON.load(File.read(node_config_path)))
  # And expands out the roles to all of their recipes
  full_run_list = node.expand!('disk')

  # Iterate over all the recipes in the runlist, which can be either "cookbook" or
  # "cookbook::subrecipe" -- we only want "cookbook"
  cookbooks = full_run_list.recipes.map {|recipe|
    # sets the short cookbook name
    original = recipe =~ /(.+)::[^:]*/ ? $1 : recipe
    # load all the "depends" from metadata as well.
    dependencies = cl[original].metadata.dependencies.keys
    # return both
    [original, dependencies]
  }.flatten.uniq # flatten and uniq the array.

  # do some bookkeeping to setup a run context, which is used to keep track of
  # which dependencies have already been loaded.
  events = Chef::EventDispatch::Dispatcher.new
  cookbook_collection = Chef::CookbookCollection.new(cl)
  run_context = Chef::RunContext.new(node, cookbook_collection, events)

  # This loads the attributes for each cookbook into the node
  compiler = Chef::RunContext::CookbookCompiler.new(run_context, full_run_list, events)
  compiler.compile_libraries
  compiler.compile_resource_definitions
  compiler.compile_lwrps
  compiler.compile_attributes

  node
end