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
  condition.each_node(:begin, *EQUALS_ASGN_NODES) do |asgn_node|
    # skip safe assignment nodes if safe assignment is allowed
    return if safe_assignment_allowed? && safe_assignment?(asgn_node)
    # 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