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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::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. The cop does not make an assessment if the return type is unknown (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.

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

# 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

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::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

#conservative? ⇒ Boolean (readonly, private)

[ GitHub ] 

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 210



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 104



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) || non_comparison_call?(value)
  end
end


  








  

    #all_return_values_boolean?(return_values)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 132



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 98



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


  








  

    #and_or?(node)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 187



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


  








  

    #boolean_return?(value)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 139



def boolean_return?(value)
  value.boolean_type? || (value.call_type? && value.comparison_method?)
end


  








  

    #extract_and_or_clauses(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 191



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 198



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`.
    node.branches.filter_map { |branch| branch ? last_value(branch) : s(:nil) }
  end
end


  








  

    #extract_return_value(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 157



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 170



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


  








  

    #non_comparison_call?(value)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 114



def non_comparison_call?(value)
  value.call_type? && !value.comparison_method?
end


  








  

    #on_def(node)  
    Also known as: #on_defs
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 82



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 94



alias on_defs on_def


  








  

    #potential_non_predicate?(return_values)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/naming/predicate_method.rb', line 143



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 175



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 118



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