Add a rule prefer-exact-props

[julienw]

With react and flow, it's very common to type props like this:

type Props = {
  prop1: string,
  prop2: number
};

However this makes it possible to pass other props as well, as by default objects in Flow are not exact. So this can hide an issue where the developer removed a prop but the caller still use it:

<Component prop1='foo' prop2={42} prop3='bar' />

Or made a typo (this example is possible is prop2 is optional):

<Component prop1='foo' porp2={42} />

To fix this with flow, the solution is to use exact objects:

type Props = {|
  prop1: string,
  prop2: number
|};

It would be useful to have an eslint rule to force this pattern.

[ljharb]

I'm a bit hesitant to have Flow-only rules in a non-flow-specific eslint plugin, but I agree that such a rule would be a good thing to have if using Flow.

With PropTypes, you can use https://npmjs.com/prop-types-exact to get the same behavior; maybe the rule could recommend both?

[julienw]

Ah yep, good idea !