Support TS 3.9 @ts-expect-error comment?

[karlhorky]

Hi @ikatyang,

First of all, thanks for the awesome project, really useful!

I was wondering what your feelings are on supporting the // @ts-expect-error comments from TypeScript 3.9.

Right now, my test files have errors in them (in the editor), because the lines after // @dts-jest:fail:snap should actually have an error:

What I would like to be able to do would be to use // @ts-expect-error either in the place of:

// @ts-expect-error
mergeArrays([]);

...or in addition to the dts-jest annotations:

// @dts-jest:fail:snap
// @ts-expect-error
mergeArrays([]);

or...

// @ts-expect-error
// @dts-jest:fail:snap
mergeArrays([]);

or even...

// @ts-expect-error @dts-jest:fail:snap
mergeArrays([]);

...none of which currently work.

Not sure if this is a feasible ask actually, but it would be nice to clean up more errors in my project!

[karlhorky]

Wow, super fast @ikatyang, thanks! I'll upgrade now!

[karlhorky]

Ah, just trying this out, I guess this doesn't allow using snapshots. I guess that means I need to remove my snapshots when upgrading to this.

I suppose this is not super critical, but it would be nice to be able to configure that as well, in case it should test against the snapshot:

// @ts-expect-error @dts-jest:fail:snap

Regarding compatibility, the rest of the line after @ts-ignore or @ts-expect-error is recommended to be used to describe why the error is being suppressed, which seems to fit this use case:

It is recommended practice to have the remainder of the comment following @ts-ignore explain which error is being suppressed.

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-6.html#suppress-errors-in-ts-files-using--ts-ignore-comments

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In case you're open to this, but it would be a feature for later, I can also open a new issue for this.

[ikatyang]

Ah, sorry. I did not explain what the new usage is. Basically, @ts-expect-error is treated as an alias of @dts-jest:fail, which means you could use // @ts-expect-error:snap [description] to replace // @dts-jest:fail:snap [description], and snapshots are still supported for sure.

Let me know if you have any question.

[karlhorky]

Ohh, didn't catch the [flags] in the readme there, sorry! Should have seen that.

Edit: I've opened a quick PR to add an example for that: #390