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`:
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.
@example
# bad def some_method some_var = 1 do_something end
@example
# good def some_method some_var = 1 do_something(some_var) end
Constants
- MSG
Public Class Methods
joining_forces()
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 36 def self.joining_forces VariableForce end
Public Instance Methods
after_leaving_scope(scope, _variable_table)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 40 def after_leaving_scope(scope, _variable_table) scope.variables.each_value { |variable| check_for_unused_assignments(variable) } end
check_for_unused_assignments(variable)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 44 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(location, message: message) end end
collect_variable_like_names(scope)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 108 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)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 62 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)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 68 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)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 78 def multiple_assignment_message(variable_name) " Use `_` or `_#{variable_name}` as a variable name to indicate " \ "that it won't be used." end
operator_assignment_message(scope, assignment)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 83 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.sub(/=$/, '')}` " \ "instead of `#{assignment.operator}`." 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 98 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
similar_name_message(variable)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 91 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)
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# File lib/rubocop/cop/lint/useless_assignment.rb, line 117 def variable_like_method_invocation?(node) return false unless node.send_type? node.receiver.nil? && !node.arguments? end