4.4 has incorrect output (.d.ts) when inferred from JSX proptypes

[frehner]

Bug Report

🔎 Search Terms

proptypes
4.4 proptypes
prop types
proptype function

🕗 Version & Regression Information

• This changed between versions 4.3.5 and 4.4

⏯ Playground Link

4.3 playground

declare function Select({ myFunc }: {
    myFunc?: any;
}): JSX.Element;

Now see the difference with 4.4 playground

declare function Select({ myFunc }: {
    myFunc?: null | undefined;
}): JSX.Element;

myFunc is no longer allowed to be, well, anything except null/undefined, when it should be any

Note that this appears to happen in 4.4 when I turn on strictNullChecks - if you turn that toggle off in 4.4, it goes back to the myFunc?: any; def, so there appears to be something going on there maybe? I can't tell if this is some sort of interaction with the new exactOptionalPropertyTypes toggle or what, though if I turn that off in 4.4 it still doesn't change the .d.ts. So 🤷

💻 Code

import React from 'react'
import PropTypes from 'prop-types'

const Select = ({myFunc = null}) => {
  return <button onClick={() => myFunc?.()}>hi</button>
}

Select.propTypes = {
  myFunc: PropTypes.func
}

export default Select

🙁 Actual behavior

myFunc?: null | undefined;

myFunc is only allowed to be null | undefined

🙂 Expected behavior

myFunc?: any;

myFunc is any

---

From reading the release blog post, I don't notice anything that would appear to change this behavior. I could have misunderstood or missed it though!

[frehner]

Appears to still happen in 4.5 beta https://www.typescriptlang.org/play?strictNullChecks=true&ts=4.5.0-beta&filetype=js#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wChRJY4AFHMAFQE8wkBnObXAsOgWhmZsypNBAB2reAGUkAGyQY4AXjgAKAN4hGAMQCuYtMrhjds2QF8AlMoB8cdaThwiMXVDFwAPACNdMGOJw4gDCssBoANZK6qrWSnZaegYA-AB0seY2ABbAngD0vv7iNqTmpKQy8hipPBAMguwqDk6J+mgAXDR0TCysqZhtpeVIAB6U8AAmSJgoptJyCjBAA

[weswigham]

So first, nothing about this is related to JSX. The much simpler

export const Select = ({myFunc = null}) => {
  myFunc?.();
}

is enough to show the change in the declaration emit/errors on myFunc?.().

Second, this regressed in #43933, definitely intentionally. Under strictNullChecks, an explicit null assignment makes the default inferred type be null, not any.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.