TS may parse type parameter lists as JSX

[AlexStacker]

TS may mistakenly use generics as jsx，but it's ok on vscode.

TypeScript Version: 3.0.1

Search Terms:
jsx generics, class generics

Code

const a = <T = any>(): Array<T> => {
    return;
}

Expected behavior:

Actual behavior:

Playground Link:
compile errror:
https://agentcooper.github.io/typescript-play/?jsx=1#code/MYewdgzgLgBAhjAvDAPAFSfMBPAfACgEoAuGAQQCcK5t1cl6BvAWACgYOYKBTKAVwpgA3GwC+QA

but code on this is OK

[basarat]

Its known : https://basarat.gitbooks.io/typescript/content/docs/jsx/react.html#generic-functions

I'm a user just like you just wanted to state that users have known this in the past 🌹

[AlexStacker]

@basarat Thank you very much for your reply and solved my doubts. If the official can improve this problem, then I feel would be useful.

[DanielRosenwasser]

I think we should be able to use lookahead to detect that we definitely have a type parameter list.

[RyanCavanaugh]

We already do some lookahead to look for a comma after the <T; we should also look for =. Note that extends is not a sufficient lookahead becase <foo extends></foo> is legal JSX

[jakebailey]

This was fixed in #47112, so #47062 was a dupe of this one.