class RuboCop::Cop::Style::NonNilCheck

end
!current_user.nil?
def signed_in?
# good
Non-nil checks are allowed if they are the final nodes of predicate.
end
if x
# good (when allowing semantic changes)
end
if !x.nil?
# bad (when allowing semantic changes)
# good (when not allowing semantic changes)
end
if x != nil
# bad
@example
This cop checks for non-nil checks, which are usually redundant.

def autocorrect(node) 

def autocorrect(node)
  case node.method_name
  when :!=
    autocorrect_comparison(node)
  when :!
    autocorrect_non_nil(node, node.receiver)
  when :nil?
    autocorrect_unless_nil(node, node.receiver)
  end
end

def autocorrect_comparison(node) 

def autocorrect_comparison(node)
  expr = node.source
  new_code = if include_semantic_changes?
               expr.sub(/\s*!=\s*nil/, '')
             else
               expr.sub(/^(\S*)\s*!=\s*nil/, '!\1.nil?')
             end
  return if expr == new_code
  ->(corrector) { corrector.replace(node.source_range, new_code) }
end

def autocorrect_non_nil(node, inner_node) 

def autocorrect_non_nil(node, inner_node)
  lambda do |corrector|
    if inner_node.receiver
      corrector.replace(node.source_range, inner_node.receiver.source)
    else
      corrector.replace(node.source_range, 'self')
    end
  end
end

def autocorrect_unless_nil(node, receiver) 

def autocorrect_unless_nil(node, receiver)
  lambda do |corrector|
    corrector.replace(node.parent.loc.keyword, 'if')
    corrector.replace(node.source_range, receiver.source)
  end
end

def include_semantic_changes? 

def include_semantic_changes?
  cop_config['IncludeSemanticChanges']
end

def message(node) 

def message(node)
  if node.method?(:!=)
    'Prefer `!expression.nil?` over `expression != nil`.'
  else
    'Explicit non-nil checks are usually redundant.'
  end
end

def on_def(node) 

def on_def(node)
  body = node.body
  return unless node.predicate_method? && body
  if body.begin_type?
    ignore_node(body.children.last)
  else
    ignore_node(body)
  end
end

def on_send(node) 

def on_send(node)
  return if ignored_node?(node)
  if not_equal_to_nil?(node)
    add_offense(node, location: :selector)
  elsif include_semantic_changes? &&
        (not_and_nil_check?(node) || unless_and_nil_check?(node))
    add_offense(node)
  end
end

def unless_and_nil_check?(send_node) 

def unless_and_nil_check?(send_node)
  parent = send_node.parent
  nil_check?(send_node) && unless_check?(parent) && !parent.ternary? &&
    parent.unless?
end