class RuboCop::Cop::Lint::UselessAssignment
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.
Constants
- MSG
Public Instance Methods
after_leaving_scope(scope, _variable_table)
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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
check_for_unused_assignments(variable)
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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.source_range else assignment.node.loc.name end add_offense(nil, location, message) end end
collect_variable_like_names(scope)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 80 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
join_force?(force_class)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 19 def join_force?(force_class) force_class == VariableForce end
message_for_useless_assignment(assignment)
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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
return_value_node_of_scope(scope)
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TODO: More precise handling (rescue, ensure, nested begin, etc.)
# 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
variable_like_method_invocation?(node)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 92 def variable_like_method_invocation?(node) return false unless node.send_type? receiver, _method_name, *args = *node receiver.nil? && args.empty? end