puppetlabs/puppet · error · ArgumentError

%{option} default_to requires a block

Error message

%{option} default_to requires a block

What it means

OptionBuilder#default_to registers the block that lazily computes an option's default; calling it without a block raises ArgumentError (lib/puppet/interface/option_builder.rb:98). The block is stored via Option#default= and evaluated when the action is invoked, so a literal block is mandatory.

Source

Thrown at lib/puppet/interface/option_builder.rb:98

  end

  # Sets whether the option is required. If no argument is given it
  # defaults to setting it as a required option.
  # @api public
  # @dsl Faces
  def required(value = true)
    @option.required = value
  end

  # Sets a block that will be used to compute the default value for this
  # option. It will be evaluated when the action is invoked. The block
  # should take no arguments.
  # @api public
  # @dsl Faces
  def default_to(&block)
    unless block
      # TRANSLATORS 'default_to' is a method name and should not be translated
      raise ArgumentError, _("%{option} default_to requires a block") % { option: @option }
    end
    if @option.has_default?
      raise ArgumentError, _("%{option} already has a default value") % { option: @option }
    end
    unless block.arity == 0
      # TRANSLATORS 'default_to' is a method name and should not be translated
      raise ArgumentError, _("%{option} default_to block should not take any arguments") % { option: @option }
    end

    @option.default = block
  end
end

View on GitHub (pinned to e227c27540)

Solutions

1. Pass a literal block: `default_to { 'production' }`
2. For computed values keep the block argument-free: `default_to { Puppet.settings[:environment] }`
3. Guard optional defaults: `default_to { config[:default] } if config.key?(:default)`

Example fix

# before
option "--environment" do
  default_to
end

# after
option "--environment" do
  default_to { "production" }
end

# when the default comes from a variable
raise ArgumentError, 'default_to needs a block' if default_proc.nil?
default_to(&default_proc) # inside the option block

When it happens

Trigger: `option '--foo' do default_to end` (no block); `default_to(&config[:default])` where the config value is nil.

Common situations: Placeholder DSL left from scaffolding; defaults sourced from a config hash whose key is absent.

Related errors

• %{option} before_action requires a block
• %{option} after_action requires a block
• %{name} can't be optional and have a default value
• default value for %{name} is a %{class_name}, not a proc
• before action hook for %{name} is a %{class_name}, not a pro

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/0a40739744e91cc8. Report an issue: GitHub.