Missing trailing comma in TSX arrow single type param

[nicolo-ribaudo]

Prettier 2.5.1
Playground link

--parser babel-ts

Input:

let arr = <T,>() => <div></div>;

Output:

let arr = <T>() => <div></div>;

Expected behavior:

It should print the trailing comma.

let arr = <T,>() => <div></div>;

When using TSX, arrow functions with a single type argument must have a trailing comma to disambiguate it from JSX. Babel currently has a bug and parses <T>() => <div></div>, but TS doesn't. We are fixing the Babel bug at babel/babel#14135.

[kachkaev]

Looks like a duplicate of #6114 and #6302. You can try writing let arr = <T,>() => <div></div>; in Example.tsx and the comma will preserve.

[nicolo-ribaudo]

In the playground link it's not preserved 🤔

[nicolo-ribaudo]

Oh I see, even if the playground parses TSX it doesn't not print as if the output file was .tsx.

[tianyingchun]

it seems that this issue also can be reproduce. #12479 (comment)

writing let arr = <T,>(s:T) =>

{s}

; in Example.tsx and the comma will preserve. works fine.