Adding a jsx comment causes TypeScript to identify children type as any[], even though generated javascript doesn't change

[lxe]

TypeScript Version: 3.3.3 - 4.0.5

Search Terms:

Typescript jsx comment any[] children

Code

Playground

import * as React from 'react';

declare var SomeComponent: React.FC<{
    children?: React.ReactElement
}>;

function Good () {
    // Yields React.createElement(SomeComponent, null, React.createElement("div", null)));
    // This satisfies TypeScript
    return <SomeComponent>
        <div />
    </SomeComponent>
}

function Bad () {
    // Still yields React.createElement(SomeComponent, null, React.createElement("div", null)));
    // This does NOT satisfy TypeScript type checking:
    // Type '{ children: any[]; }' is not assignable to type '{ children?: ReactElement<...'.
    return <SomeComponent>
        {/* Comment */}
        <div />
    </SomeComponent>
}

Expected behavior:

The case without a JSX comment and the case with a comment both yield the same JavaScript (e.g. the comment does not count as an extra child). TypeScript should understand that the type of <div /> matches the expected signature React.ReactElement

Actual behavior:

However, when the JSX comment is present, even though the resulting JS is the same, TypeScript now assumes the type to be any[] which no longer satisfies React.ReactElement.

Playground Link: Link

Related Issues:

• https://stackoverflow.com/questions/64667775/is-it-possible-to-prevent-jsx-comment-from-adding-a-children-element-potentia
• "Ignore this error message" code fix in JSX results in rendering // @ts-ignore #27552 (comment)

[MartinJohns]

Very likely a duplicate of #41125.

[lxe]

Thanks @MartinJohns that's gotta be it! No issues in nightly! Playground.

Does this mean this will be mainlined in 4.1 or do we have to wait until February 2021 for this to be available in 4.2?

Feel free to tag and close.

[RyanCavanaugh]

Things merged prior to last week will be in 4.1. Thanks!

[typescript-bot]

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