class RuboCop::Cop::Style::StringLiterals

def detect_quote_styles(node)
  styles = node.children.map { |c| c.loc.begin }
  # For multi-line strings that only have quote marks
  # at the beginning of the first line and the end of
  # the last, the begin and end region of each child
  # is nil. The quote marks are in the parent node.
  return [node.loc.begin.source] if styles.all?(&:nil?)
  styles.map(&:source).uniq
end