class RuboCop::Cop::Style::FormatString

argument is an array literal.
if the first argument is a string literal and if the second
manner for all cases, so only two scenarios are considered -
The detection of String#% cannot be implemented in a reliable
Valid options include Kernel#format, Kernel#sprintf and String#%.
This cop enforces the use of a single string formatting utility.

def message(detected_style) 

def message(detected_style)
  format(MSG, method_name(style), method_name(detected_style))
end

def method_name(style_name) 

def method_name(style_name)
  style_name == :percent ? 'String#%' : style_name
end

def on_send(node) 

def on_send(node)
  return unless (selector = formatter(node))
  detected_style = selector == :% ? :percent : selector
  return if detected_style == style
  add_offense(node, :selector, message(detected_style))
end