[TypeScript] Assert fail

[jaejun-choi]

Bug Report

Current Behavior
Code fails with Babel, but it works with TSC

Input Code

type x = string
<div></div>

Error: Assert fail
    at assert (@babel/parser/lib/index.js:8543:11)
    at _class.parseMaybeAssign (@babel/parser/lib/index.js:10196:9)
...

Babel Configuration (.babelrc, package.json, cli command)

• typescript
• jsx

Environment

• Babel version(s): 7.1.2
• Node/npm version: Node 8.12 / npm 6.4.1
• OS: Linux Mint 18.3

[babel-bot]

Hey @jj-choi! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
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[woongsikchoi]

This issue also occurs when merge conflict message like "<<<<<<< HEAD" occurs after TypeScript interface declaration.

interface Foo { }
<<<<<<< HEAD

[JakeGinnivan]

Found another example of this error:

const tern
let assignMe

tern ? (assignMe = <div />) : (assignMe = <div>Doesn't work</div>)

An inline ternary which assigns JSX to a variable. It is only the else path which causes the Assert fail.

[armano2]

this issue seem to be fixed in jsx or when react preset is enabled

[nicolo-ribaudo]

Fixed by #12599, thanks!