class RuboCop::Cop::Style::MutableConstant

Checks whether some constant value isn’t a mutable literal (e.g. array or hash).

Strict mode can be used to freeze all constants, rather than just literals. Strict mode is considered an experimental feature. It has not been updated with an exhaustive list of all methods that will produce frozen objects so there is a decent chance of getting some false positives. Luckily, there is no harm in freezing an already frozen object.

From Ruby 3.0, this cop honours the magic comment ‘shareable_constant_value’. When this magic comment is set to any acceptable value other than none, it will suppress the offenses raised by this cop. It enforces frozen state.

NOTE: Regexp and Range literals are frozen objects since Ruby 3.0.

NOTE: From Ruby 3.0, interpolated strings are not frozen when ‘# frozen-string-literal: true` is used, so this cop enforces explicit freezing for such strings.

NOTE: From Ruby 3.0, this cop allows explicit freezing of constants when the ‘shareable_constant_value` directive is used.

@safety

This cop's autocorrection is unsafe since any mutations on objects that
are made frozen will change from being accepted to raising `FrozenError`,
and will need to be manually refactored.

@example EnforcedStyle: literals (default)

# bad
CONST = [1, 2, 3]

# good
CONST = [1, 2, 3].freeze

# good
CONST = <<~TESTING.freeze
  This is a heredoc
TESTING

# good
CONST = Something.new

@example EnforcedStyle: strict

# bad
CONST = Something.new

# bad
CONST = Struct.new do
  def foo
    puts 1
  end
end

# good
CONST = Something.new.freeze

# good
CONST = Struct.new do
  def foo
    puts 1
  end
end.freeze

@example

# Magic comment - shareable_constant_value: literal

# bad
CONST = [1, 2, 3]

# good
# shareable_constant_value: literal
CONST = [1, 2, 3]

Constants

MSG

Public Instance Methods

on_casgn(node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 127
def on_casgn(node)
  _scope, _const_name, value = *node
  if value.nil? # This is only the case for `CONST += ...` or similarg66
    parent = node.parent
    return unless parent.or_asgn_type? # We only care about `CONST ||= ...`

    value = parent.children.last
  end

  on_assignment(value)
end

Private Instance Methods

autocorrect(corrector, node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 169
def autocorrect(corrector, node)
  expr = node.source_range

  splat_value = splat_value(node)
  if splat_value
    correct_splat_expansion(corrector, expr, splat_value)
  elsif node.array_type? && !node.bracketed?
    corrector.wrap(expr, '[', ']')
  elsif requires_parentheses?(node)
    corrector.wrap(expr, '(', ')')
  end

  corrector.insert_after(expr, '.freeze')
end
check(value) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 158
def check(value)
  range_enclosed_in_parentheses = range_enclosed_in_parentheses?(value)
  return unless mutable_literal?(value) ||
                (target_ruby_version <= 2.7 && range_enclosed_in_parentheses)

  return if frozen_string_literal?(value)
  return if shareable_constant_value?(value)

  add_offense(value) { |corrector| autocorrect(corrector, value) }
end
correct_splat_expansion(corrector, expr, splat_value) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 208
def correct_splat_expansion(corrector, expr, splat_value)
  if range_enclosed_in_parentheses?(splat_value)
    corrector.replace(expr, "#{splat_value.source}.to_a")
  else
    corrector.replace(expr, "(#{splat_value.source}).to_a")
  end
end
frozen_regexp_or_range_literals?(node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 200
def frozen_regexp_or_range_literals?(node)
  target_ruby_version >= 3.0 && (node.regexp_type? || node.range_type?)
end
immutable_literal?(node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 190
def immutable_literal?(node)
  frozen_regexp_or_range_literals?(node) || node.immutable_literal?
end
mutable_literal?(value) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 184
def mutable_literal?(value)
  return false if frozen_regexp_or_range_literals?(value)

  value.mutable_literal?
end
on_assignment(value) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 141
def on_assignment(value)
  if style == :strict
    strict_check(value)
  else
    check(value)
  end
end
requires_parentheses?(node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 204
def requires_parentheses?(node)
  node.range_type? || (node.send_type? && node.loc.dot.nil?)
end
shareable_constant_value?(node) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 194
def shareable_constant_value?(node)
  return false if target_ruby_version < 3.0

  recent_shareable_value? node
end
strict_check(value) click to toggle source
# File lib/rubocop/cop/style/mutable_constant.rb, line 149
def strict_check(value)
  return if immutable_literal?(value)
  return if operation_produces_immutable_object?(value)
  return if frozen_string_literal?(value)
  return if shareable_constant_value?(value)

  add_offense(value) { |corrector| autocorrect(corrector, value) }
end