TypeScript generics are removed incorrectly

[JounQin]

Prettier 1.16.2
Playground link

--parser typescript

Input:

export default {
  load<K, T>(k: K, t: T) {
  	return {k, t};
  }
}

Output:

export default {
  load(k: K, t: T) {
    return { k, t };
  }
};

Expected behavior:
preserve TypeScript generics

[ikatyang]

Regression from #5799.

cc @JamesHenry

[ikatyang]

@JounQin Sorry for the inconvenience, the temporary workaround (#5818) is released in 1.16.3.

Prettier 1.16.3
Playground link

--parser typescript

Input:

export default {
  load<K, T>(k: K, t: T) {
  	return {k, t};
  }
}

Output:

export default {
  load<K, T>(k: K, t: T) {
    return { k, t };
  }
};

[JamesHenry]

Thanks for pushing out a patch @ikatyang, I'm guessing we were just missing coverage for this in the prettier tests?

I can work on it and restore the updated version of typescript-estree

[ikatyang]

Yeah, we probably just need to fix this missing case. It's still the updated version (the OP can be reproduced) on master as I only reverted it in the 1.16 branch.

[j-f1]

This is because the parser puts the typeParamaters on the Property node rather than the FunctionExpression.

[Jessidhia]

That sounds like a parser bug to me; it's not otherwise possible to have any kind of generics on properties 🤔

But if it works...

[JamesHenry]

@j-f1 Did you not see this? #5817 (comment)

I worked on this, just hadn't opened a PR yet.

I found the AST oddity yesterday and @armano2 and I agreed that it shouldn't be the case and we need to diverge from babel there (and report it)

[j-f1]

Should I close this PR then?

[JamesHenry]

No, it's the same solution, but obviously want to avoid situations where multiple people are doing the same work

[j-f1]

Yeah, I didn’t see your comment when I was making the PR. Sorry about that.

[JamesHenry]

All good 👍

[armano2]

looks like there is few more issues here:

export class {
  constructor<T, X, F>(k: K, t: T) {
  	return {k, t};
  }
}

[JamesHenry]

Oh wow, merging the PR on the other repo caused this issue to be closed. I'm guessing it piggybacked my permissions on both repos? Don't think I've ever seen that before

[j-f1]

Yeah, that’s one of the features of GitHub that comes in handy every so often.

[brodybits]

I think this issue is now resolved by PR #6027 (TS 3.4 update which includes @typescript-eslint/typescript-estree version 1.6.0).

[evilebottnawi]

I think we need merge test before close this to avoid regressions in future

[brodybits]

I think we need merge test before close this to avoid regressions in future

The commit I proposed in PR #5989 should automatically close this issue as resolved and tested.

Thanks @evilebottnawi for your attention:)