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Class: RuboCop::Cop::Naming::PredicateMethod

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
self, ::RuboCop::Cop::AllowedPattern, ::RuboCop::Cop::AllowedMethods, ::RuboCop::Cop::Base, ::RuboCop::Cop::AutocorrectLogic, ::RuboCop::Cop::IgnoredNode, ::RuboCop::Util, RuboCop::AST::Sexp
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/naming/predicate_method.rb

Overview

Checks that predicate methods end with ? and non-predicate methods do not.

The names of predicate methods (methods that return a boolean value) should end in a question mark. Methods that don’t return a boolean, shouldn’t end in a question mark.

The cop assesses a predicate method as one that returns boolean values. Likewise, a method that only returns literal values is assessed as non-predicate. Other predicate method calls are assumed to return boolean values. The cop does not make an assessment if the return type is unknown (non-predicate method calls, variables, etc.).

Note
 Operator methods (def ==, etc.) are ignored.

By default, the cop runs in conservative mode, which allows a method to be named with a question mark as long as at least one return value is boolean. In aggressive mode, methods with a question mark will register an offense if any known non-boolean return values are detected.

The cop also has ::RuboCop::Cop::AllowedMethods configuration in order to prevent the cop from registering an offense from a method name that does not confirm to the naming guidelines. By default, call is allowed. The cop also has AllowedPatterns configuration to allow method names by regular expression.

Although returning a call to another predicate method is treated as a boolean value, certain method names can be known to not return a boolean, despite ending in a ? (for example, Numeric#nonzero? returns self or nil). These methods can be configured using NonBooleanPredicates.

The cop can furthermore be configured to allow all bang methods (method names ending with !), with AllowBangMethods: true (default false).

Examples:

Mode: conservative (default)

# bad
def foo
  bar == baz
end

# good
def foo?
  bar == baz
end

# bad
def foo?
  5
end

# good
def foo
  5
end

# bad
def foo
  x == y
end

# good
def foo?
  x == y
end

# bad
def foo
  !x
end

# good
def foo?
  !x
end

# bad - returns the value of another predicate method
def foo
  bar?
end

# good
def foo?
  bar?
end

# good - operator method
def ==(other)
  hash == other.hash
end

# good - at least one return value is boolean
def foo?
  return unless bar?
  true
end

# ok - return type is not known
def foo?
  bar
end

# ok - return type is not known
def foo
  bar?
end

Mode: aggressive

# bad - the method returns nil in some cases
def foo?
  return unless bar?
  true
end

AllowBangMethods: false (default)

# bad
def save!
  true
end

AllowBangMethods: true

# good
def save!
  true
end

Constant Summary

::RuboCop::Cop::Base - Inherited

EMPTY_OFFENSES, RESTRICT_ON_SEND

Class Attribute Summary

::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 a 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

::RuboCop::Cop::AllowedMethods - Included

#ignored_method?

::RuboCop::Cop::Base - Inherited

#active_support_extensions_enabled?, #always_autocorrect?, #config, #config_to_allow_offenses, #config_to_allow_offenses=, #contextual_autocorrect?, #processed_source, #string_literals_frozen_by_default?, #target_satisfies_all_gem_version_requirements?

::RuboCop::Cop::AutocorrectLogic - Included

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #autocorrect_with_disable_uncorrectable?, #correctable?, #disable_uncorrectable?, #safe_autocorrect?

Instance Method Summary

::RuboCop::Cop::AllowedPattern - Included

#allowed_line?, #allowed_patterns, #cop_config_deprecated_methods_values, #cop_config_patterns_values, #ignored_line?, #matches_allowed_pattern?, #matches_ignored_pattern?

::RuboCop::Cop::AllowedMethods - Included

#allowed_method?, #allowed_methods, #cop_config_allowed_methods, #cop_config_deprecated_values

::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_gem_version

Returns a gems locked versions (i.e.
#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

#disable_offense, #disable_offense_at_end_of_line, #disable_offense_before_and_after, #disable_offense_with_eol_or_surround_comment, #eol_comment, #eol_comment_would_be_inside_literal?, #heredoc_range, #line_with_eol_comment_too_long?, #max_line_length, #multiline_ranges, #multiline_string?,
#range_by_lines

Expand the given range to include all of any lines it covers.
#range_of_first_line, #string_continuation?, #surrounding_heredoc?, #surrounding_percent_array?

::RuboCop::Cop::IgnoredNode - Included

#ignore_node, #ignored_node?, #part_of_ignored_node?, #ignored_nodes

Constructor Details

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

Instance Attribute Details

#allow_bang_methods? ⇒ Boolean (readonly, private)

[ GitHub ] 

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 289



def allow_bang_methods?
  cop_config.fetch('AllowBangMethods', false)
end


  








  

    #conservative?  ⇒ Boolean  (readonly, private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 279



def conservative?
  cop_config.fetch('Mode', :conservative).to_sym == :conservative
end


  







Instance Method Details



  

    #acceptable?(return_values)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 159



def acceptable?(return_values)
  # In `conservative` mode, if the method returns `super`, `zsuper`, or a
  # non-comparison method call, the method name is acceptable.
  return false unless conservative?

  return_values.any? do |value|
    value.type?(:super, :zsuper) || unknown_method_call?(value)
  end
end


  








  

    #all_return_values_boolean?(return_values)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 189



def all_return_values_boolean?(return_values)
  values = return_values.reject { |value| value.type?(:super, :zsuper) }
  return false if values.empty?

  values.all? { |value| boolean_return?(value) }
end


  








  

    #allowed?(node)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 151



def allowed?(node)
  allowed_method?(node.method_name) ||
    matches_allowed_pattern?(node.method_name) ||
    allowed_bang_method?(node) ||
    node.operator_method? ||
    node.body.nil?
end


  








  

    #allowed_bang_method?(node)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 283



def allowed_bang_method?(node)
  return false unless allow_bang_methods?

  node.bang_method?
end


  








  

    #and_or?(node)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 253



def and_or?(node)
  node.type?(:and, :or)
end


  








  

    #boolean_return?(value)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 196



def boolean_return?(value)
  return true if value.boolean_type?

  method_returning_boolean?(value)
end


  








  

    #extract_and_or_clauses(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 257



def extract_and_or_clauses(node)
  # Recursively traverse an `and` or `or` node to collect all clauses within
  return node unless and_or?(node)

  [extract_and_or_clauses(node.lhs), extract_and_or_clauses(node.rhs)].flatten
end


  








  

    #extract_conditional_branches(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 264



def extract_conditional_branches(node)
  return node unless node.conditional?

  if node.type?(:while, :until)
    # If there is no body, act as implicit `nil`.
    node.body ? [last_value(node.body)] : [s(:nil)]
  else
    # Branches with no value act as an implicit `nil`.
    branches = node.branches.map { |branch| branch ? last_value(branch) : s(:nil) }
    # Missing else branches also act as an implicit `nil`.
    branches.push(s(:nil)) unless node.else_branch
    branches
  end
end


  








  

    #extract_return_value(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 223



def extract_return_value(node)
  return node unless node.return_type?

  # `return` without a value is a `nil` return.
  return s(:nil) if node.arguments.empty?

  # When there's a multiple return, it cannot be a predicate
  # so just return an `array` sexp for simplicity.
  return s(:array) unless node.arguments.one?

  node.first_argument
end


  








  

    #last_value(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 236



def last_value(node)
  value = node.begin_type? ? node.children.last : node
  value&.return_type? ? extract_return_value(value) : value
end


  








  

    #method_returning_boolean?(value)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 202



def method_returning_boolean?(value)
  return false unless value.call_type?
  return false if wayward_predicate?(value.method_name)

  value.comparison_method? || value.predicate_method? || value.negation_method?
end


  








  

    #on_def(node)  
    Also known as: #on_defs
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 135



def on_def(node)
  return if allowed?(node)

  return_values = return_values(node.body)
  return if acceptable?(return_values)

  if node.predicate_method? && potential_non_predicate?(return_values)
    add_offense(node.loc.name, message: MSG_NON_PREDICATE)
  elsif !node.predicate_method? && all_return_values_boolean?(return_values)
    add_offense(node.loc.name, message: MSG_PREDICATE)
  end
end


  








  

    #on_defs(node)  
  



  

    


Alias for #on_def.



  



  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 147



alias on_defs on_def


  








  

    #potential_non_predicate?(return_values)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 209



def potential_non_predicate?(return_values)
  # Assumes a method to be non-predicate if all return values are non-boolean literals.
  #
  # In `Mode: conservative`, if any of the return values is a boolean,
  # the method name is acceptable.
  # In `Mode: aggressive`, all return values must be booleans for a predicate
  # method, or else an offense will be registered.
  return false if conservative? && return_values.any? { |value| boolean_return?(value) }

  return_values.any? do |value|
    value.literal? && !value.boolean_type?
  end
end


  








  

    #process_return_values(return_values)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 241



def process_return_values(return_values)
  return_values.flat_map do |value|
    if value.conditional?
      process_return_values(extract_conditional_branches(value))
    elsif and_or?(value)
      process_return_values(extract_and_or_clauses(value))
    else
      value
    end
  end
end


  








  

    #return_values(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 175



def return_values(node)
  # Collect all the (implicit and explicit) return values of a node
  return_values = Set.new(node.begin_type? ? [] : [extract_return_value(node)])

  node.each_descendant(:return) do |return_node|
    return_values << extract_return_value(return_node)
  end

  last_value = last_value(node)
  return_values << last_value if last_value

  process_return_values(return_values)
end


  








  

    #unknown_method_call?(value)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 169



def unknown_method_call?(value)
  return false unless value.call_type?

  !method_returning_boolean?(value)
end


  








  

    #wayward_predicate?(name)  ⇒ Boolean  (private)
  



  

    


If a method ending in ? is known to not return a boolean value,
(for example, Numeric#nonzero?) it should be treated as a non-boolean
value, despite the method naming.



  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 296



def wayward_predicate?(name)
  wayward_predicates.include?(name.to_s)
end


  








  

    #wayward_predicates   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 300



def wayward_predicates
  Array(cop_config.fetch('WaywardPredicates', []))
end