流-缓存公共变量检查时,读取联合类型属性不起作用

在里面 this example ,Flow向我们展示了根据类型读取属性的方法。

我将其重构为如下所示,并按预期工作:

type Success = { success: true, value: boolean };
type Failed  = { success: false, error: string };

type Response = Success | Failed;

function handleResponse(response: Response) {
  const value = response.success && response.value;
  const error = !response.success && response.error;
}

但是,当公共属性是字符串时,它在执行 === 检查,但如果将检查缓存到变量中,则不会:

type Success2 = { success: 'success', value: boolean };
type Failed2  = { success: 'not_success', error: string };

type Response2 = Success | Failed;

function handleResponse(response: Response2) {
  const isSuccess = response.success === 'success';

  // const value = response.success === 'success' && response.value;  // WORK

  const value = isSuccess && response.value;  // DOESN'T WORK
}

换句话说,必须有 === 在读取变量之前检查(字面意思),不能将其包含在变量中。

这是已知的流量限制,还是我遗漏了什么?