JSX spread doesn't work with union props

TypeScript Version: 2.4.0 / nightly (2.5.0-dev.201xxxxx)

It's often useful to define a React component's properties as a union type, e.g.

type InfoProps =
  | { status: 'hidden' }
  | { status: 'visible'; content: string }

const Info = (props: InfoProps) =>
  props.status === 'hidden'
    ? <noscript />
    : <div>{props.content}</div>

When constructing elements from this component, it works fine in concrete cases:

<Info status="hidden" />
<Info status="visible" content="hello world" />

however if you try to use "spread" syntax, it's a type error:

declare const infoProps: InfoProps

<Info {...infoProps} />
/* .  ^^^^^^^^^^^^^^
Type '{ status: "hidden" | "visible"; }' is not assignable to type '(IntrinsicAttributes & { status: "hidden"; }) | (IntrinsicAttributes & { status: "visible"; conte...'.
  Type '{ status: "hidden" | "visible"; }' is not assignable to type 'IntrinsicAttributes & { status: "visible"; content: string; }'.
    Type '{ status: "hidden" | "visible"; }' is not assignable to type '{ status: "visible"; content: string; }'.
      Types of property 'status' are incompatible.
        Type '"hidden" | "visible"' is not assignable to type '"visible"'.
          Type '"hidden"' is not assignable to type '"visible"'.
*/

As I understand it, this should be no different semantically from

React.createElement(Info, infoProps)

which the compiler approves of.

Just hit on exactly the same problem, reproducible in 2.4.1 and 2.5.2. Another example:

import React, { SFC } from 'react';

{
    type CommonProps = { common: string };
    type Props = CommonProps &
        ({ type: 'foo' } | { type: 'bar'; message: string });

    const Button: SFC<Props> = (props) => null;

    const OtherButton1: SFC<Props> = (props) => React.createElement(Button, props);

    // Type '"foo"' is not assignable to type '"bar"'.
    const OtherButton2: SFC<Props> = (props) => <Button {...props} />;
}

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JSX spread doesn't work with union props #18670

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JSX spread doesn't work with union props #18670

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OliverJAsh commented on Sep 25, 2017

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