class RuboCop::Cop::Style::IfUnlessModifier

The maximum line length is configurable.
if written as a modifier if/unless.
Checks for if and unless statements that would fit on one line

def message(keyword) 

def message(keyword)
  "Favor modifier `#{keyword}` usage when having a single-line body." \
  ' Another good alternative is the usage of control flow `&&`/`||`.'
end

def on_if(node) 

def on_if(node)
  # discard ternary ops, if/else and modifier if/unless nodes
  return if ternary_op?(node)
  return if modifier_if?(node)
  return if elsif?(node)
  return if if_else?(node)
  return unless fit_within_line_as_modifier_form?(node)
  add_offense(node, :keyword, message(node.loc.keyword.source))
end