Example custom fact for Facter 3+ with 2 implementations

modules.rb

Facter.add(:modules) do

  setcode { simple }

  def simple
    codedir = Facter::Core::Execution.exec('puppet config print codedir')
    list = Facter::Core::Execution.exec("ls #{codedir}/modules").split("\n")
    {
      count: list.size,
      list: list.freeze
    }
  end

  def power
    require 'yaml'
    require 'puppet'
    yaml = Facter::Core::Execution.exec('puppet module list --render-as yaml')
    data = YAML.load(yaml)

    modules = []
    data[:'modules_by_path'].each do |k, list|
      list.each do |m|
        splited = m.forge_name.split('/')
        modules.push({
          name: m.forge_name,
          company: splited[0],
          short: splited[1],
          version: m.version
        })
      end
    end
    {
      list: modules,
      names: {
        full: modules.map { |m| m[:name] },
        short: modules.map { |m| m[:short] }
      },
      count: modules.size
    }
  end
end