class RSpec::Matchers::DSL::Matcher

def singleton_method_added(name)
  return unless @block_method_differentiator
  if @block_method_differentiator.instance_methods.include?(name)
    add_deprecation_warning_to(name,
      "Calling a helper method (`#{name}`) defined as an instance method (using `def #{name}`) as a macro from a custom matcher `define` block",
      "`def self.#{name}` (to define it as a singleton method)",
      "defined in the custom matcher definition block",
      :unless
    )
  elsif @block_method_differentiator.singleton_methods.include?(name)
    add_deprecation_warning_to(name,
      "Calling a helper method (`#{name}`) defined as a singleton method (using `def self.#{name}`) on a custom matcher",
      "`def #{name}` (to define it as an instance method)",
      "defined in the custom matcher definition block",
      :if
    )
  end
end