class RuboCop::Cop::Lint::UselessAssignment
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.
@example
# bad def some_method some_var = 1 do_something end # good def some_method some_var = 1 do_something(some_var) end
Constants
- MSG
Public Class Methods
# File lib/rubocop/cop/lint/useless_assignment.rb, line 47 def self.joining_forces VariableForce end
Public Instance Methods
# 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
rubocop:disable Metrics/AbcSize
# File lib/rubocop/cop/lint/useless_assignment.rb, line 165 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 106 def chained_assignment?(node) node.respond_to?(:expression) && node.expression&.lvasgn_type? end
rubocop:disable Metrics/AbcSize, Metrics/PerceivedComplexity, Metrics/CyclomaticComplexity
# 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 149 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
rubocop:enable Metrics/AbcSize, Metrics/PerceivedComplexity, Metrics/CyclomaticComplexity
# 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 110 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 120 def multiple_assignment_message(variable_name) " Use `_` or `_#{variable_name}` as a variable name to indicate " \ "that it won't be used." end
# 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 125 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
rubocop:enable Metrics/AbcSize
# File lib/rubocop/cop/lint/useless_assignment.rb, line 182 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 206 def remove_local_variable_assignment_part(corrector, node) corrector.replace(node, node.expression.source) end
# File lib/rubocop/cop/lint/useless_assignment.rb, line 195 def remove_trailing_character_from_operator(corrector, node) corrector.remove(node.parent.location.operator.end.adjust(begin_pos: -1)) end
# File lib/rubocop/cop/lint/useless_assignment.rb, line 191 def rename_variable_with_underscore(corrector, node) corrector.replace(node, '_') end
# File lib/rubocop/cop/lint/useless_assignment.rb, line 199 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
TODO: More precise handling (rescue, ensure, nested begin, etc.)
# File lib/rubocop/cop/lint/useless_assignment.rb, line 139 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
# 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 132 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
# File lib/rubocop/cop/lint/useless_assignment.rb, line 158 def variable_like_method_invocation?(node) return false unless node.send_type? node.receiver.nil? && !node.arguments? end