This cop checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ruby -cw :
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.
'Useless assignment to variable - `%s`.'
MINIMUM_SIMILARITY_TO_SUGGEST =
This class inherits a constructor from RuboCop::Cop::Cop
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 23 def after_leaving_scope(scope, _variable_table) scope.variables.each_value do |variable| check_for_unused_assignments(variable) end end
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 29 def check_for_unused_assignments(variable) return if variable.should_be_unused? variable.assignments.each do |assignment| next if assignment.used? message = message_for_useless_assignment(assignment) location = if assignment.regexp_named_capture? assignment.node.children.first.loc.expression else assignment.node.loc.name end add_offense(nil, location, message) end end
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 93 def collect_variable_like_names(scope) names = scope.each_node.with_object(Set.new) do |node, set| if variable_like_method_invocation?(node) _receiver, method_name, = *node set method_name end end variable_names = scope.variables.each_value.map(&:name) names.merge(variable_names) end
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 80 def find_similar_name(target_name, scope) names = collect_variable_like_names(scope) names.delete(target_name) scores = names.each_with_object(>) do |name, hash| score = StringUtil.similarity(target_name, name) hash[name] = score if score >= MINIMUM_SIMILARITY_TO_SUGGEST end most_similar_name, _max_score = scores.max_by |_, score| score > most_similar_name end
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 47 def message_for_useless_assignment(assignment) variable = assignment.variable message = format(MSG, variable.name) if assignment.multiple_assignment? message " Use `_` or `_#variable.name>` as a variable name " \ "to indicate that it won't be used." elsif assignment.operator_assignment? return_value_node = return_value_node_of_scope(variable.scope) if assignment.meta_assignment_node.equal?(return_value_node) non_assignment_operator = assignment.operator.sub(/=$/, '') message " Use just operator `#non_assignment_operator>`." end else similar_name = find_similar_name(variable.name, variable.scope) message " Did you mean `#similar_name>`?" if similar_name end message end
TODO: More precise handling (rescue, ensure, nested begin, etc.)
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 70 def return_value_node_of_scope(scope) body_node = scope.body_node if body_node.type == :begin body_node.children.last else body_node end end
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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 105 def variable_like_method_invocation?(node) return false unless node.send_type? receiver, _method_name, *args = *node receiver.nil? && args.empty? end