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Class: RuboCop::Cop::Metrics::ParameterLists

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

Overview

Checks for methods with too many parameters.

The maximum number of parameters is configurable. Keyword arguments can optionally be excluded from the total count, as they add less complexity than positional or optional parameters.

Any number of arguments for initialize method inside a block of Struct.new and Data.define like this is always allowed:

Struct.new(:one, :two, :three, :four, :five, keyword_init: true) do
  def initialize(one:, two:, three:, four:, five:)
  end
end

This is because checking the number of arguments of the initialize method does not make sense.

Note
Explicit block argument &block is not counted to prevent erroneous change that is avoided by making block argument implicit.

This cop also checks for the maximum number of optional parameters. This can be configured using the MaxOptionalParameters config option.

Examples:

Max: 3

# good
def foo(a, b, c = 1)
end

Max: 2

# bad
def foo(a, b, c = 1)
end

CountKeywordArgs: true (default)

# counts keyword args towards the maximum

# bad (assuming Max is 3)
def foo(a, b, c, d: 1)
end

# good (assuming Max is 3)
def foo(a, b, c: 1)
end

CountKeywordArgs: false

# don't count keyword args towards the maximum

# good (assuming Max is 3)
def foo(a, b, c, d: 1)
end

MaxOptionalParameters: 3 (default)

# good
def foo(a = 1, b = 2, c = 3)
end

MaxOptionalParameters: 2

# bad
def foo(a = 1, b = 2, c = 3)
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 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::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 Attribute Details

#count_keyword_args?Boolean (readonly, private)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 141

def count_keyword_args?
  cop_config['CountKeywordArgs']
end

Instance Method Details

#args_count(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 125

def args_count(node)
  if count_keyword_args?
    node.children.count { |a| !a.blockarg_type? }
  else
    node.children.count { |a| !NAMED_KEYWORD_TYPES.include?(a.type) && !a.blockarg_type? }
  end
end

#argument_to_lambda_or_proc?(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 121

def_node_matcher :argument_to_lambda_or_proc?, <<~PATTERN
  ^lambda_or_proc?
PATTERN

#max_optional_parameters (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 137

def max_optional_parameters
  cop_config['MaxOptionalParameters']
end

#max_params (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 133

def max_params
  cop_config['Max']
end

#on_args(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 104

def on_args(node)
  parent = node.parent
  return if parent.method?(:initialize) && struct_new_or_data_define_block?(parent.parent)

  count = args_count(node)
  return unless count > max_params

  return if argument_to_lambda_or_proc?(node)

  add_offense(node, message: format(MSG, max: max_params, count: args_count(node))) do
    self.max = count
  end
end

#on_def(node) Also known as: #on_defs

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 90

def on_def(node)
  optargs = node.arguments.select(&:optarg_type?)
  return if optargs.count <= max_optional_parameters

  message = format(
    OPTIONAL_PARAMETERS_MSG,
    max: max_optional_parameters,
    count: optargs.count
  )

  add_offense(node, message: message) { self.max_optional_parameters = optargs.count }
end

#on_defs(node)

Alias for #on_def.

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 102

alias on_defs on_def

#struct_new_or_data_define_block?(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/metrics/parameter_lists.rb', line 81

def_node_matcher :struct_new_or_data_define_block?, <<~PATTERN
  (block
    {
      (send (const {nil? cbase} :Struct) :new ...)
      (send (const {nil? cbase} :Data) :define ...)
    }
    (args) ...)
PATTERN