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Class: RuboCop::Cop::Style::DoubleNegation

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::AutoCorrector, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/style/double_negation.rb

Overview

Checks for uses of double negation (!!) to convert something to a boolean value.

When using EnforcedStyle: allowed_in_returns, allow double negation in contexts that use boolean as a return value. When using EnforcedStyle: forbidden, double negation should be forbidden always.

Note
when something is a boolean value !!something and !something.nil? are not the same thing. As you’re unlikely to write code that can accept values of any type this is rarely a problem in practice.

Examples:

# bad
!!something

# good
!something.nil?

EnforcedStyle: allowed_in_returns (default)

# good
def foo?
  !!return_value
end

define_method :foo? do
  !!return_value
end

define_singleton_method :foo? do
  !!return_value
end

EnforcedStyle: forbidden

# bad
def foo?
  !!return_value
end

define_method :foo? do
  !!return_value
end

define_singleton_method :foo? do
  !!return_value
end

Cop Safety Information:

  • Autocorrection is unsafe when the value is false, because the result of the expression will change.

    !!false     #=> false
    !false.nil? #=> true

Constant Summary

::RuboCop::Cop::Base - Inherited

EMPTY_OFFENSES, RESTRICT_ON_SEND

::RuboCop::Cop::ConfigurableEnforcedStyle - Included

SYMBOL_TO_STRING_CACHE

Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,
.support_autocorrect?

Returns if class supports autocorrect.

.support_multiple_source?

Override if your cop should be called repeatedly for multiple investigations Between calls to on_new_investigation and on_investigation_end, the result of processed_source will remain constant.

Class Method Summary

::RuboCop::Cop::Base - Inherited

.autocorrect_incompatible_with

List of cops that should not try to autocorrect at the same time as this cop.

.badge

Naming.

.callbacks_needed, .cop_name, .department,
.documentation_url

Returns an url to view this cops documentation online.

.exclude_from_registry

Call for abstract Cop classes.

.inherited,
.joining_forces

Override and return the Force class(es) you need to join.

.match?

Returns true if the cop name or the cop namespace matches any of the given names.

.new,
.requires_gem

Register a version requirement for the given gem name.

.restrict_on_send

::RuboCop::ExcludeLimit - Extended

exclude_limit

Sets up a configuration option to have an exclude limit tracked.

transform

Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::ConfigurableEnforcedStyle - Included

::RuboCop::Cop::Base - Inherited

#add_global_offense

Adds an offense that has no particular location.

#add_offense

Adds an offense on the specified range (or node with an expression) Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense.

#begin_investigation

Called before any investigation.

#callbacks_needed,
#cop_config

Configuration Helpers.

#cop_name, #excluded_file?,
#external_dependency_checksum

This method should be overridden when a cop’s behavior depends on state that lives outside of these locations:

#inspect
#message

Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.

#name

Alias for Base#cop_name.

#offenses,
#on_investigation_end

Called after all on_…​

#on_new_investigation

Called before all on_…​

#on_other_file

Called instead of all on_…​

#parse

There should be very limited reasons for a Cop to do it’s own parsing.

#parser_engine,
#ready

Called between investigations.

#relevant_file?, #target_rails_version, #target_ruby_version, #annotate, #apply_correction, #attempt_correction,
#callback_argument

Reserved for Cop::Cop.

#complete_investigation

Called to complete an investigation.

#correct, #current_corrector,
#current_offense_locations

Reserved for Commissioner:

#current_offenses, #currently_disabled_lines, #custom_severity, #default_severity, #disable_uncorrectable, #enabled_line?, #file_name_matches_any?, #find_message, #find_severity, #range_for_original, #range_from_node_or_range,
#reset_investigation

Actually private methods.

#use_corrector

::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

This class inherits a constructor from RuboCop::Cop::Base

Instance Method Details

#allowed_in_returns?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 84

def allowed_in_returns?(node)
  node.parent&.return_type? || end_of_method_definition?(node)
end

#define_method?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 111

def define_method?(node)
  return false unless node.block_type?

  child = node.child_nodes.first
  return false unless child.send_type?

  child.method?(:define_method) || child.method?(:define_singleton_method)
end

#double_negative?(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 69

def_node_matcher :double_negative?, '(send (send _ :!) :!)'

#double_negative_condition_return_value?(node, last_child, conditional_node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 138

def double_negative_condition_return_value?(node, last_child, conditional_node)
  parent = find_parent_not_enumerable(node)
  if parent.begin_type?
    node.loc.line == parent.loc.last_line
  else
    last_child.last_line <= conditional_node.last_line
  end
end

#end_of_method_definition?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 88

def end_of_method_definition?(node)
  return false unless (def_node = find_def_node_from_ascendant(node))

  conditional_node = find_conditional_node_from_ascendant(node)
  last_child = find_last_child(def_node.send_type? ? def_node : def_node.body)

  if conditional_node
    double_negative_condition_return_value?(node, last_child, conditional_node)
  elsif last_child.pair_type? || last_child.hash_type? || last_child.parent.array_type?
    false
  else
    last_child.last_line <= node.last_line
  end
end

#find_conditional_node_from_ascendant(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 120

def find_conditional_node_from_ascendant(node)
  return unless (parent = node.parent)
  return parent if parent.conditional?

  find_conditional_node_from_ascendant(parent)
end

#find_def_node_from_ascendant(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 103

def find_def_node_from_ascendant(node)
  return unless (parent = node.parent)
  return parent if parent.def_type? || parent.defs_type?
  return node.parent.child_nodes.first if define_method?(parent)

  find_def_node_from_ascendant(node.parent)
end

#find_last_child(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 127

def find_last_child(node)
  case node.type
  when :rescue
    find_last_child(node.body)
  when :ensure
    find_last_child(node.child_nodes.first)
  else
    node.child_nodes.last
  end
end

#find_parent_not_enumerable(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 147

def find_parent_not_enumerable(node)
  return unless (parent = node.parent)

  if parent.pair_type? || parent.hash_type? || parent.array_type?
    find_parent_not_enumerable(parent)
  else
    parent
  end
end

#on_send(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/double_negation.rb', line 71

def on_send(node)
  return unless double_negative?(node) && node.prefix_bang?
  return if style == :allowed_in_returns && allowed_in_returns?(node)

  location = node.loc.selector
  add_offense(location) do |corrector|
    corrector.remove(location)
    corrector.insert_after(node, '.nil?')
  end
end