puppetlabs/puppet · error · Puppet::Pops::Types::StringConverter::FormatError

Illegal format '#{actual}' specified for value of Type type

Error message

Illegal format '#{actual}' specified for value of Type type - expected one of the characters 'sp'

What it means

StringConverter raises this FormatError when formatting a Type value (PTypeType — the value itself is a type like Integer[0,10]) with a conversion letter other than 's' (type's string form, quoted with alt flag) or 'p' (same via Kernel.format). The else at string_converter.rb:1113 raises FormatError('Type', f.format, 'sp'). Types stringify to their notation (e.g. 'Integer[0, 10]') and support no other conversions.

Source

Thrown at lib/puppet/pops/types/string_converter.rb:1113

    end
  end

  # @api private
  def string_PStructType(val_type, val, format_map, indentation)
    string_PHashType(val_type, val, format_map, indentation)
  end

  # @api private
  def string_PTypeType(val_type, val, format_map, _)
    f = get_format(val_type, format_map)
    case f.format
    when :s
      str_val = f.alt? ? "\"#{val}\"" : val.to_s
      Kernel.format(f.orig_fmt, str_val)
    when :p
      Kernel.format(f.orig_fmt.tr('p', 's'), val.to_s)
    else
      raise FormatError.new('Type', f.format, 'sp')
    end
  end

  # @api private
  def string_PURIType(val_type, val, format_map, indentation)
    f = get_format(val_type, format_map)
    case f.format
    when :p
      fmt = TypeFormatter.singleton
      indentation = indentation.indenting(f.alt? || indentation.is_indenting?)
      fmt = fmt.indented(indentation.level, 2) if indentation.is_indenting?
      fmt.string(val)
    when :s
      str_val = val.to_s
      Kernel.format(f.orig_fmt, f.alt? ? puppet_quote(str_val) : str_val)
    else
      raise FormatError.new('URI', f.format, 'sp')
    end

View on GitHub (pinned to e227c27540)

Solutions

Use '%s' or '%p' when stringifying a Type value
If you need the inner type's features, extract and format its parameters instead of the type itself
Whitelist dynamic format letters against %w[s p]

Example fix

# before
$str = String($type, '%d')
# after
$str = String($type, '%s')

Defensive patterns

Strategy: validation

Validate before calling

fmt = '%d'
letter = fmt[/\A%[#\-+ 0\d.]*([a-zA-Z])\z/, 1]
raise ArgumentError, "#{fmt} invalid for Type values" unless %w[s p].include?(letter)

Prevention

Only %s and %p render Type values
When generating messages about types, interpolate with String($type, '%p')
Keep type objects out of data destined for numeric/other formatting

When it happens

Trigger: `String(Integer, '%d')`, `String($type_var, '%q')` — any letter except s/p applied to a value whose inferred type is Type[...]; common when echoing parameter types in error messages or generated docs.

Common situations: Building validation error text that interpolates the expected type with a generic formatter; debug output walking heterogeneous data that includes type objects.

Related errors

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/4cc5cf18572a5357. Report an issue: GitHub.