class RuboCop::Cop::Lint::AssignmentInCondition

if/while/until.
This cop checks for assignments in the conditions of

def check(node) 

def check(node)
  condition, = *node
  # assignments inside blocks are not what we're looking for
  return if condition.type == :block
  traverse_node(condition, ASGN_TYPES) do |asgn_node|
    if asgn_node.type == :send
      _receiver, method_name, *_args = *asgn_node
      next :skip_children if method_name != :[]=
    end
    # skip safe assignment nodes if safe assignment is allowed
    if safe_assignment_allowed? && safe_assignment?(asgn_node)
      next :skip_children
    end
    # assignment nodes from shorthand ops like ||= don't have operator
    if asgn_node.type != :begin && asgn_node.loc.operator
      add_offense(asgn_node, :operator)
    end
  end
end

def on_if(node) 

def on_if(node)
  check(node)
end

def on_until(node) 

def on_until(node)
  check(node)
end

def on_while(node) 

def on_while(node)
  check(node)
end

def traverse_node(node, types, &block)

each_node/visit_descendants_with_types with :skip_children 
def traverse_node(node, types, &block)
  result = yield node if types.include?(node.type)
  # return to skip all descendant nodes
  return if result == :skip_children
  node.children.each do |child|
    traverse_node(child, types, &block) if child.is_a?(Astrolabe::Node)
  end
end