Broken jsx element with not static type with ts 3.2.1

[dfilatov]

TypeScript Version: 3.2.1

Search Terms:
jsx

Code

import * as React from 'react';

function render(url?: string): React.ReactNode {
    const Tag = url? 'a' : 'button';
    return <Tag>test</Tag>;
}

Expected behavior:
Everything is ok. TypeScript 3.1.6 compiles it properly.

Actual behavior:
error: JSX element type 'Tag' does not have any construct or call signatures. [2604]

[devrelm]

Related: #28631

[weswigham]

It's because we started strongly checking tag calls such as these, and the 'a' tag's properties and 'button' tag's properties are heavily dissimilar (one isn't a strict subset of the other) - they're all optional, so a call like this can still succeed at runtime, but in the typesystem at present the two signatures are irreconcilable. Needs a full fix of #7294 to work well.

[rhys-vdw]

Please consider this now broken example:

import React, {
  ReactType,
  StatelessComponent,
} from "react"
import classNames from "classnames"

interface Props {
  className?: string
}

export function createStyledComponent<P extends { className: string }>(
  Component: ReactType<P>,
  className: string
): StatelessComponent<Props> {
  return props => (
    <Component className={classNames(className, props.className)}>
      {props.children}
    </Component>
  )
}

ERROR in [at-loader] ./app/assets/javascripts/utilities/component-factory.tsx:19:6
    TS2604: JSX element type 'Component' does not have any construct or call signatures.

Is this something that should be addressed in @types/react?

[Jessidhia]

Nothing that can be done on the @types/react side, or rather, what can be done is already done -- ReactType<P> will work more-or-less correctly with React.createElement.

Note that your P extends { className: string } will actually reject all DOM elements because their className includes undefined which is not assignable to string.

[rhys-vdw]

@Kovensky Oops, the existing (working) code I had was:

export function createStyledComponent(
  Component: ReactType,
  className: string
): StatelessComponent<Props> {
  return props => (
    <Component className={classNames(className, props.className)}>
      {props.children}
    </Component>
  )
}

That generic change was an attempt to get it working under TS 3.2.1

[azizhk]

Just a small reproduction:
https://repl.it/repls/InconsequentialBreakableCategories
Go to package.json and change typescript version to 3.2.1 to see how this breaks.

How I had to fix it:
https://github.com/ritz078/pebble/pull/151/files#diff-288d98c45cab569122e391278589e7dbR123
But still, that does not work as something fails in the union of types. Check how InputProps union type is defined. Now I can't do something like:

const inp = (
  <Input
    textArea={abc as boolean}
  />
)

even though my union type is

type InputProps = {
  textArea?: false
  // more types where textArea would be undefined or false
} & {
  textArea: true
  // more types where textArea would be true
}