Class: RuboCop::Cop::Lint::UselessAssignment

Inherits:
Base
  • Object
show all
Extended by:
AutoCorrector
Includes:
RangeHelp
Defined in:
lib/rubocop/cop/lint/useless_assignment.rb

Overview

Checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ‘ruby -cw`:

source,console

assigned but unused variable - foo

Currently this cop has advanced logic that detects unreferenced reassignments and properly handles varied cases such as branch, loop, rescue, ensure, etc.

This cop’s autocorrection avoids cases like ‘a ||= 1` because removing assignment from operator assignment can cause `NameError` if this assignment has been used to declare a local variable. For example, replacing `a ||= 1` with `a || 1` may cause “undefined local variable or method `a’ for main:Object (NameError)”.

NOTE: Given the assignment ‘foo = 1, bar = 2`, removing unused variables can lead to a syntax error, so this case is not autocorrected.

Examples:

 # bad def some_method some_var = 1 do_something end # good def some_method some_var = 1 do_something(some_var) end

Constant Summary collapse

MSG = 
'Useless assignment to variable - `%<variable>s`.'

Constants included from RangeHelp

RangeHelp::BYTE_ORDER_MARK, RangeHelp::NOT_GIVEN

Constants inherited from Base

Base::RESTRICT_ON_SEND

Instance Attribute Summary

Attributes inherited from Base

#config, #processed_source

Class Method Summary collapse

Instance Method Summary collapse

Methods included from AutoCorrector

support_autocorrect?

Methods inherited from Base

#active_support_extensions_enabled?, #add_global_offense, #add_offense, #always_autocorrect?, autocorrect_incompatible_with, badge, #begin_investigation, #callbacks_needed, callbacks_needed, #config_to_allow_offenses, #config_to_allow_offenses=, #contextual_autocorrect?, #cop_config, cop_name, #cop_name, department, documentation_url, exclude_from_registry, #excluded_file?, #external_dependency_checksum, inherited, #initialize, #inspect, lint?, match?, #message, #offenses, #on_investigation_end, #on_new_investigation, #on_other_file, #parse, #parser_engine, #ready, #relevant_file?, requires_gem, #string_literals_frozen_by_default?, support_autocorrect?, support_multiple_source?, #target_gem_version, #target_rails_version, #target_ruby_version

Methods included from ExcludeLimit

#exclude_limit

Methods included from AutocorrectLogic

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

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

silence_warnings

Constructor Details

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

Class Method Details

.joining_forces ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 47 def self.joining_forces VariableForce end

Instance Method Details

#after_leaving_scope(scope, _variable_table) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 51 def after_leaving_scope(scope, _variable_table) scope.variables.each_value { |variable| check_for_unused_assignments(variable) } end

#autocorrect(corrector, assignment) ⇒ Object

rubocop:disable Metrics/AbcSize

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 167 def autocorrect(corrector, assignment) if assignment.exception_assignment? remove_exception_assignment_part(corrector, assignment.node) elsif assignment.multiple_assignment? || assignment.rest_assignment? || assignment.for_assignment? rename_variable_with_underscore(corrector, assignment.node) elsif assignment.operator_assignment? remove_trailing_character_from_operator(corrector, assignment.node) elsif assignment.regexp_named_capture? replace_named_capture_group_with_non_capturing_group(corrector, assignment.node, assignment.variable.name) else remove_local_variable_assignment_part(corrector, assignment.node) end end

#chained_assignment?(node) ⇒ Boolean

Returns:

  • (Boolean) 
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 106 def chained_assignment?(node) return true if node.lvasgn_type? && node.expression&.send_type? node.respond_to?(:expression) && node.expression&.lvasgn_type? end

#check_for_unused_assignments(variable) ⇒ Object

rubocop:disable Metrics/AbcSize, Metrics/PerceivedComplexity, Metrics/CyclomaticComplexity

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 56 def check_for_unused_assignments(variable) return if variable.should_be_unused? variable.assignments.reverse_each do |assignment| assignment_node = assignment.node next if assignment.used? || part_of_ignored_node?(assignment_node) message = message_for_useless_assignment(assignment) range = offense_range(assignment) add_offense(range, message: message) do |corrector| # In cases like `x = 1, y = 2`, where removing a variable would cause a syntax error,  # and where changing `x ||= 1` to `x = 1` would cause `NameError`,  # the autocorrect will be skipped, even if the variable is unused.  if sequential_assignment?(assignment_node) || assignment_node.parent&.or_asgn_type? next end autocorrect(corrector, assignment) end ignore_node(assignment_node) if chained_assignment?(assignment_node) end end

#collect_variable_like_names(scope) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 151 def collect_variable_like_names(scope) names = scope.each_node.with_object(Set.new) do |node, set| set << node.method_name if variable_like_method_invocation?(node) end variable_names = scope.variables.each_value.map(&:name) names.merge(variable_names) end

#message_for_useless_assignment(assignment) ⇒ Object

rubocop:enable Metrics/AbcSize, Metrics/PerceivedComplexity, Metrics/CyclomaticComplexity

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 82 def message_for_useless_assignment(assignment) variable = assignment.variable format(MSG, variable: variable.name) + message_specification(assignment, variable).to_s end

#message_specification(assignment, variable) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 112 def message_specification(assignment, variable) if assignment.multiple_assignment? multiple_assignment_message(variable.name) elsif assignment.operator_assignment? operator_assignment_message(variable.scope, assignment) else similar_name_message(variable) end end

#multiple_assignment_message(variable_name) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 122 def multiple_assignment_message(variable_name) " Use `_` or `_#{variable_name}` as a variable name to indicate " \ "that it won't be used." end

#offense_range(assignment) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 88 def offense_range(assignment) if assignment.regexp_named_capture? assignment.node.children.first.source_range else assignment.node.loc.name end end

#operator_assignment_message(scope, assignment) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 127 def operator_assignment_message(scope, assignment) return_value_node = return_value_node_of_scope(scope) return unless assignment.meta_assignment_node.equal?(return_value_node) " Use `#{assignment.operator.delete_suffix('=')}` instead of `#{assignment.operator}`." end

#remove_exception_assignment_part(corrector, node) ⇒ Object

rubocop:enable Metrics/AbcSize

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 184 def remove_exception_assignment_part(corrector, node) corrector.remove( range_between( (node.parent.children.first&.source_range || node.parent.location.keyword).end_pos, node.source_range.end_pos ) ) end

#remove_local_variable_assignment_part(corrector, node) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 208 def remove_local_variable_assignment_part(corrector, node) corrector.replace(node, node.expression.source) end

#remove_trailing_character_from_operator(corrector, node) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 197 def remove_trailing_character_from_operator(corrector, node) corrector.remove(node.parent.location.operator.end.adjust(begin_pos: -1)) end

#rename_variable_with_underscore(corrector, node) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 193 def rename_variable_with_underscore(corrector, node) corrector.replace(node, '_') end

#replace_named_capture_group_with_non_capturing_group(corrector, node, variable_name) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 201 def replace_named_capture_group_with_non_capturing_group(corrector, node, variable_name) corrector.replace( node.children.first, node.children.first.source.sub(/\(\?<#{variable_name}>/, '(?:') ) end

#return_value_node_of_scope(scope) ⇒ Object

TODO: More precise handling (rescue, ensure, nested begin, etc.)

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 141 def return_value_node_of_scope(scope) body_node = scope.body_node if body_node.begin_type? body_node.children.last else body_node end end

#sequential_assignment?(node) ⇒ Boolean

Returns:

  • (Boolean) 
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 96 def sequential_assignment?(node) if node.lvasgn_type? && node.expression&.array_type? && node.each_descendant.any?(&:assignment?) return true end return false unless node.parent sequential_assignment?(node.parent) end

#similar_name_message(variable) ⇒ Object 

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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 134 def similar_name_message(variable) variable_like_names = collect_variable_like_names(variable.scope) similar_name = NameSimilarity.find_similar_name(variable.name, variable_like_names) " Did you mean `#{similar_name}`?" if similar_name end

#variable_like_method_invocation?(node) ⇒ Boolean

Returns:

  • (Boolean) 
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 160 def variable_like_method_invocation?(node) return false unless node.send_type? node.receiver.nil? && !node.arguments? end