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

Illegal format '#{actual}' specified for value of Default ty

Error message

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

What it means

StringConverter raises this FormatError when formatting the special `default` value (PDefaultType) with a format character outside 'dDsp': 'd'/'s' render 'default', 'D' renders 'Default', 'p' quotes per Puppet notation, with alt-flag (#) variants adding quotes. Any other letter hits the else at string_converter.rb:638 and raises FormatError('Default', f.format, 'dDsp').

Source

Thrown at lib/puppet/pops/types/string_converter.rb:638

  # Basically string_PAnyType converts the value to a String and then formats it according
  # to the resulting type
  #
  # @api private
  def string_PAnyType(val_type, val, format_map, _)
    f = get_format(val_type, format_map)
    Kernel.format(f.orig_fmt, val)
  end

  def string_PDefaultType(val_type, val, format_map, _)
    f = get_format(val_type, format_map)
    apply_string_flags(f, case f.format
                          when :d, :s, :p
                            f.alt? ? '"default"' : 'default'
                          when :D
                            f.alt? ? '"Default"' : 'Default'
                          else
                            raise FormatError.new('Default', f.format, 'dDsp')
                          end)
  end

  # @api private
  def string_PUndefType(val_type, val, format_map, _)
    f = get_format(val_type, format_map)
    apply_string_flags(f, case f.format
                          when :n
                            f.alt? ? 'null' : 'nil'
                          when :u
                            f.alt? ? 'undefined' : 'undef'
                          when :d, :x, :X, :o, :b, :B, :e, :E, :f, :g, :G, :a, :A
                            'NaN'
                          when :v
                            'n/a'
                          when :V
                            'N/A'
                          when :s

View on GitHub (pinned to e227c27540)

Solutions

Use '%d', '%D', '%s' or '%p' when stringifying `default`
Branch before formatting: `if $v == default { ... } else { String($v, $fmt) }`
Check the value against the allowed letters when the format is user/data supplied

Example fix

# before
$str = String(default, '%v')
# after
$str = String(default, '%s')

Defensive patterns

Strategy: validation

Validate before calling

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

Prevention

Handle `default` explicitly (case/if) before applying generic formatting to option values
Remember %v is legal for Undef but illegal for Default
Whitelist format letters per type when formats are data-driven

When it happens

Trigger: `String(default, '%v')`, `String(default, '%t')` or any conversion letter not in d/D/s/p applied to the Puppet `default` value; a format map applied uniformly to a data structure that happens to contain `default` entries.

Common situations: Iterating heterogeneous option hashes where one entry is `default` and applying a single format string to all values; porting sprintf-style templates that use %v (which is legal for Undef but not for Default).

Related errors

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/2edda4ed7fe65dce. Report an issue: GitHub.