flowtype - "exponentially large number of cases"最新流中的错误，具有常见的传播模式

Question

我经常使用以下模式来创建对象 null/undefined省略属性:

const whatever = {
  something: true,
  ...(a ? { a } : null),
  ...(b ? { b } : null),
};

从流程版本 v0.112 开始，这会导致错误消息:

Computing object literal [1] may lead to an exponentially large number of cases to reason about because conditional [2] and conditional [3] are both unions. Please use at most one union type per spread to simplify reasoning about the spread result. You may be able to get rid of a union by specifying a more general type that captures all of the branches of the union.

在我看来，这并不是真正的类型错误，只是 Flow 试图避免一些繁重的计算。这导致我的项目中出现了数十个流程错误，我需要以某种方式解决这些错误。是否有一些优雅的方法可以为这些提供更好的类型信息？我不想修改代码的逻辑，我相信它会按照我需要的方式工作(除非有人在这里也有更优雅的解决方案)。在我求助之前在这里问 // $FlowFixMe对于所有这些。

Complete example on Try Flow

Answer 1

写起来并不优雅，我认为 Flow 应该处理你所展示的情况，但如果你仍然希望 Flow 对它进行类型检查，你可以尝试像这样重写它:

/* @flow */

type A = {
  cat: number,
};

type B = {
  dog: string,
}

type Built = {
  something: boolean,
  a?: A,
  b?: B,
};

function buildObj(a?: ?A, b?: ?B): Built {
  const ret: Built = {
    something: true
  };

  if(a) ret.a = a
  if(b) ret.b = b

  return ret;
}

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