class T::Private::Methods::DeclBuilder

def override(allow_incompatible: false)
  check_live!
  case decl.mode
  when Modes.standard
    decl.mode = Modes.override
    decl.override_allow_incompatible = allow_incompatible
  when Modes.override
    raise BuilderError.new(".override cannot be repeated in a single signature")
  else
    raise BuilderError.new("`.override` cannot be combined with any of `.abstract`, `.implementation`, or "\
          "`.overridable`.")
  end
  self
end