Typescript: TSX @ts-ignore comments no longer suppressing errors in TypeScript 3.9

[brieb]

TypeScript Version: 3.9.0-beta and 3.9.0-dev.20200330

Search Terms:

ts-ignore 3.9 tsx @ts-ignore

Code

      {/*
      // @ts-ignore */}
      <MyOtherComponent prop={123} />

Expected behavior:

Error suppressed when running tsc (TS 3.8 behavior)

Actual behavior:

Error emitted when running tsc

Repro Repo Link:

https://github.com/brieb/ts-39-issue-ts-ignore-tsx

[brieb]

I was trying to help beta test TypeScript 3.9 and we have some @ts-ignores in our TSX code that are no longer being respected, so we aren't able to get a passing build to assess performance improvements. Let us know if there is a workaround for this or a new build we should try out. So excited for all the new TypeScript 3.9 features! 😄
cc @DanielRosenwasser

[mohsen1]

line comments still work:

        <Comp
            // @ts-ignore
            badProp={1}
        />
         <Comp
            // @ts-expect-error
            badProp={1}
        />

cc @JoshuaKGoldberg

Playground

[brieb]

line comments still work

Definitely true, though is it always possible to express @ts-ignore as a line comment in TSX?
I'm trying to think of a counter example.

I suppose this is also an option if the error is on the component

    <
    // @ts-ignore
    Comp />

Though that breaks syntax highlighting in vscode and prettier goes out of whack.

My guess is that this was an unintentional breakage.

[JoshuaKGoldberg]

Indeed, this was an unintentional breakage. Specifically the breakage was here: https://github.com/microsoft/TypeScript/pull/36014/files#diff-08a3cc4f1f9a51dbb468c2810f5229d3L1782
Sorry for bungling up your TS 3.9 usage @brieb! 😅

TypeScript _used_ to check if a line looked like // @ts-ignore on its own, regardless of whether the line was part of a multiline comment. I suspect that itself was an unintentional side effect of how it was checking for comments, and just happened to work well in the .jsx/.tsx use case?

TypeScript _now_ understands where single-line // @ts-(expect-error|ignore) directives are, and only ignores comments after any of them. I suppose a good fix would be to also understand the last line of multiline comments when that line includes a comment directive. E.g. /* \n // @ts-ignore */.

..but I'll defer to the Typescript team. Happy to send a PR if that or another strategy is approved!

[brieb]

No worries, at all! Glad we could help catch this. We're so thankful for all the great work going into the TS 3.9 release!! 😃

Ya, the format is not ideal. But, that's the best that we came up with here https://github.com/microsoft/TypeScript/issues/27552

Looks like there has been some follow-up requests about a cleaner syntax for this https://github.com/microsoft/TypeScript/issues/31147

{/* @ts-ignore */} was my preference in the original issue as well.

Though I'm not sure how much scope it would add to accept that format vs fixing up the good 'ol

{/* 
// @ts-ignore */}

[DanielRosenwasser]

My intuition tells me that if @ts-ignore appears in the last line of any comment, the following line's errors should be suppressed.

[JoshuaKGoldberg]

Swell. Just to be clear @DanielRosenwasser, is your intuition strong enough for TypeScript to accept a PR making that behavior change?

[JoshuaKGoldberg]

Ping, sorry to re-tag you @DanielRosenwasser - since TS 3.9 is close to release, is there a way this could get triaged? I would very much like to fix this regression before the major release. 🤗

[DanielRosenwasser]

I'm so sorry this didn't get triaged and fell off my radar. If you can get a PR out, we can work on through it. Ideally this would go in before the RC, but I don't think we'll have time for that.

[JoshuaKGoldberg]

Swell, thanks! 🚀 #38228 minimally adds directive parsing for multiline comments.

[DanielRosenwasser]

Thanks to everyone involved on this thread for your patience, and thanks @JoshuaKGoldberg for the quick fix!