puppetlabs/puppet · error · ArgumentError

block_param accepts max 2 arguments (type, name), got %{size

Error message

block_param accepts max 2 arguments (type, name), got %{size}.

What it means

block_param accepts zero, one, or two arguments: (), (name), or (type, name). Any third argument raises this ArgumentError at definition time. The case/size dispatch in the ParameterDsl has no branch above 2.

Source

Thrown at lib/puppet/functions.rb:488

    # Defines one required block parameter that may appear last. If type and name is missing the
    # default type is "Callable", and the name is "block". If only one
    # parameter is given, then that is the name and the type is "Callable".
    #
    # @api public
    def block_param(*type_and_name)
      case type_and_name.size
      when 0
        type = @all_callables
        name = :block
      when 1
        type = @all_callables
        name = type_and_name[0]
      when 2
        type, name = type_and_name
        type = Puppet::Pops::Types::TypeParser.singleton.parse(type, loader) unless type.is_a?(Puppet::Pops::Types::PAnyType)
      else
        raise ArgumentError, _("block_param accepts max 2 arguments (type, name), got %{size}.") % { size: type_and_name.size }
      end

      unless Puppet::Pops::Types::TypeCalculator.is_kind_of_callable?(type, false)
        raise ArgumentError, _("Expected PCallableType or PVariantType thereof, got %{type_class}") % { type_class: type.class }
      end

      unless name.is_a?(Symbol)
        raise ArgumentError, _("Expected block_param name to be a Symbol, got %{name_class}") % { name_class: name.class }
      end

      if @block_type.nil?
        @block_type = type
        @block_name = name
      else
        raise ArgumentError, _('Attempt to redefine block')
      end
    end
    alias required_block_param block_param

View on GitHub (pinned to e227c27540)

Solutions

1. Pass at most two arguments: a type reference and a Symbol name.
2. For defaults, use block_param with no arguments: the default is type Callable and name :block.
3. For an optional block with a default of nil in the method, use optional_block_param instead of extra arguments.

Example fix

# before
 block_param 'Callable', :block, 'unused'

# after
 block_param 'Callable', :block
 # or simply: block_param   -> Callable, :block

# CI grep: block_param called with three or more comma-separated arguments
! grep -rnE "block_param[[:space:]]+[^,]+,[^,]+," lib/

When it happens

Trigger: block_param 'Callable', :block, 'extra' inside a dispatch block; usually a copy-paste of a param line into block_param, or a mistaken belief that block_param takes a default value argument.

Common situations: Editing existing dispatch blocks; converting a param declaration into a block declaration and leaving extra arguments behind.

Related errors

• Attempt to redefine block
• Function Load Error for function '%{function_name}': %{messa
• A required parameter cannot be added after an optional param
• Expected PCallableType or PVariantType thereof, got %{type_c
• Expected block_param name to be a Symbol, got %{name_class}

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/de26913b325c96f8. Report an issue: GitHub.