   @doc """
   Sets Mix debug mode.
   """
+  @spec debug(boolean()) :: :ok
   def debug(debug) when is_boolean(debug) do
     Mix.State.put(:debug, debug)
   end

  Be careful when invoking this function as any project
  configuration won't be reloaded.
  """
  def target(target) when is_atom(target) do
    Mix.State.put(:target, target)
  end

  Proper configuration can be set in `Mix.Config` files, often per-environment
  (see `Mix.Config.import_config/1` for more information).
  """
  @spec env() :: atom()
  def env do
    # env is not available on bootstrapping, so set a :dev default
    Mix.State.get(:env, :dev)
