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.

@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 Instance Methods

after_leaving_scope(scope, _variable_table) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 40
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) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 46
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: location, message: message)
  end
end
collect_variable_like_names(scope) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 111
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) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 36
def join_force?(force_class)
  force_class == VariableForce
end
message_for_useless_assignment(assignment) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 64
def message_for_useless_assignment(assignment)
  variable = assignment.variable

  format(MSG, variable.name) +
    message_specification(assignment, variable).to_s
end
message_specification(assignment, variable) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 71
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) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 81
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) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 86
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) click to toggle source

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

# File lib/rubocop/cop/lint/useless_assignment.rb, line 101
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) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 95
def similar_name_message(variable)
  similar_name = find_similar_name(variable.name, variable.scope)
  " Did you mean `#{similar_name}`?" if similar_name
end
variable_like_method_invocation?(node) click to toggle source
# File lib/rubocop/cop/lint/useless_assignment.rb, line 123
def variable_like_method_invocation?(node)
  return false unless node.send_type?
  receiver, _method_name, *args = *node
  receiver.nil? && args.empty?
end