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Class: RuboCop::Cop::Lint::UnexpectedBlockArity

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/lint/unexpected_block_arity.rb

Overview

Checks for a block that is known to need more positional block arguments than are given (by default this is configured for Enumerable methods needing 2 arguments). Optional arguments are allowed, although they don’t generally make sense as the default value will be used. Blocks that have no receiver, or take splatted arguments (ie. *args) are always accepted.

Keyword arguments (including **kwargs) do not get counted towards this, as they are not used by the methods in question.

Method names and their expected arity can be configured like this:

Methods:
  inject: 2
  reduce: 2

Examples:

# bad
values.reduce {}
values.min { |a| a }
values.sort { |a; b| a + b }

# good
values.reduce { |memo, obj| memo << obj }
values.min { |a, b| a <=> b }
values.sort { |*x| x[0] <=> x[1] }

Cop Safety Information:

  • This cop matches for method names only and hence cannot tell apart methods with same name in different classes, which may lead to a false positive.

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 Method Details

#acceptable?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 63

def acceptable?(node)
  !(included_method?(node.method_name) && node.receiver)
end

#arg_count(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 75

def arg_count(node)
  return node.children[1] if node.numblock_type? # the maximum numbered param for the block

  # Only `arg`, `optarg` and `mlhs` (destructuring) count as arguments that
  # can be used. Keyword arguments are not used for these methods so are
  # ignored.
  node.arguments.count do |arg|
    return Float::INFINITY if arg.restarg_type?

    arg.arg_type? || arg.optarg_type? || arg.mlhs_type?
  end
end

#expected_arity(method) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 71

def expected_arity(method)
  cop_config['Methods'][method.to_s]
end

#included_method?(name) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 67

def included_method?(name)
  methods.key?(name.to_s)
end

#methods (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 59

def methods
  cop_config.fetch('Methods', [])
end

#on_block(node) Also known as: #on_numblock

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 44

def on_block(node)
  return if acceptable?(node)

  expected = expected_arity(node.method_name)
  actual = arg_count(node)
  return if actual >= expected

  message = format(MSG, method: node.method_name, expected: expected, actual: actual)
  add_offense(node, message: message)
end

#on_numblock(node)

Alias for #on_block.

[ GitHub ]

  
# File 'lib/rubocop/cop/lint/unexpected_block_arity.rb', line 55

alias on_numblock on_block