puppetlabs/puppet · error · ArgumentError

Expected block_param name to be a Symbol, got %{name_class}

Error message

Expected block_param name to be a Symbol, got %{name_class}

What it means

The name given to block_param must be a Symbol. With one argument that argument is taken as the name; with two, the second is the name. Passing a String (for example 'block') fails the Symbol check and raises this ArgumentError at definition time.

Source

Thrown at lib/puppet/functions.rb:496

      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

    # Defines one optional block parameter that may appear last. If type or name is missing the
    # defaults are "any callable", and the name is "block". The implementor of the dispatch target
    # must use block = nil when it is optional (or an error is raised when the call is made).
    #
    # @api public
    def optional_block_param(*type_and_name)
      # same as required, only wrap the result in an optional type

View on GitHub (pinned to e227c27540)

Solutions

1. Write the name as a Symbol: block_param 'Callable', :block.
2. With a single argument, pass the Symbol name only: block_param :block.
3. Adopt the convention that every name in a dispatch block (param names included) is written with a leading colon.

Example fix

# before
 block_param 'Callable', 'block'
 block_param 'block'

# after
 block_param 'Callable', :block
 block_param :block

# Every DSL name argument must be a Symbol
name_guard = ->(name) { name.is_a?(Symbol) }
raise ArgumentError, 'pass :block not "block"' unless name_guard.call(:block)

When it happens

Trigger: block_param 'block' (a single String is treated as the name), or block_param 'Callable', 'block'. Both leave name as a String at the is_a?(Symbol) check.

Common situations: Copy-paste of param declarations where strings are common; forgetting that DSL names in dispatch blocks are Symbols.

Related errors

• Expected PCallableType or PVariantType thereof, got %{type_c
• Parameter name argument must be a Symbol. Got %{name_class}
• block_param accepts max 2 arguments (type, name), got %{size
• Attempt to redefine block
• Argument to 'return_type' must be a String reference to a Pu

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/b07bbb805dba620d. Report an issue: GitHub.