class T::Private::Methods::DeclBuilder

def checked(level)
  if T.unsafe(true)
    raise "The .checked API is unstable, so we don't want it used until we redesign it. To change Sorbet's runtime behavior, see https://sorbet.org/docs/tconfiguration"
  end
  check_live!
  if !decl.checked.equal?(ARG_NOT_PROVIDED)
    raise BuilderError.new("You can't call .checked multiple times in a signature.")
  end
  if !decl.soft_notify.equal?(ARG_NOT_PROVIDED)
    raise BuilderError.new("You can't use .checked with .soft.")
  end
  if !decl.generated.equal?(ARG_NOT_PROVIDED)
    raise BuilderError.new("You can't use .checked with .generated.")
  end
  if !T::Private::RuntimeLevels::LEVELS.include?(level)
    raise BuilderError.new("Invalid `checked` level '#{level}'. Use one of: #{T::Private::RuntimeLevels::LEVELS}.")
  end
  decl.checked = level
  self
end