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[no-unsafe-assignment/return] Relax restrictions to allow any => unknown assignment #2325

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ghost opened this issue Jul 25, 2020 · 6 comments · Fixed by #2371
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[no-unsafe-assignment/return] Relax restrictions to allow any => unknown assignment #2325

ghost opened this issue Jul 25, 2020 · 6 comments · Fixed by #2371
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@yasarsid
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enhancement New feature or request good first issue Good for newcomers has pr there is a PR raised to close this package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin

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@ghost
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ghost commented Jul 25, 2020 •
edited by ghost
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Repro

function myFunction(): unknown {
    // triggers no-unsafe-assignment because JSON.parse returns any
    let val: unknown = JSON.parse(someStringVar);

    // triggers no-unsafe-return because JSON.parse returns any
    return JSON.parse(someStringVar);
}

Expected Result

This should not throw an error because a direct any => unknown cast cannot possibly be unsafe. Requiring an as unknown everywhere is unnecessary noise.

Additional notes

Ideally, any should not be used across a code base, and I like that the current default rules enforce this. However, a lot of existing APIs still use any, including the TypeScript library itself, and we have to make do with what we have.
@ghost ghost added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Jul 25, 2020
@bradzacher bradzacher added enhancement New feature or request good first issue Good for newcomers and removed triage Waiting for team members to take a look labels Jul 25, 2020
@bradzacher
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Happy to accept a PR!

@yasarsid
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yasarsid commented Aug 7, 2020

Hi @bradzacher - If its all right, I want to work on this.

@yasarsid yasarsid mentioned this issue Aug 7, 2020
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@bradzacher bradzacher added the has pr there is a PR raised to close this label Aug 9, 2020
@maletor
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maletor commented Aug 15, 2020

This is awesome!

But I got down a rabbit hole where you can't take 'unknown' back to a structured object like an interface.

You can take 'unknown' to 'object' but you're stuck there. Even doing 'prop in object' doesn't work.

Whats the reason? Is there a workaround?

@maletor
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maletor commented Aug 15, 2020 •
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Addendum: I found user defined type guards but those seem really error prone. What happens if the interface changes and the type guard doesn't? Seems like it's of little use for writing safe code and a olive branch for lack of real type system.

@bradzacher
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In this regard, unknown and any are the same. The difference being that unknown ensures you don't do things that are unsafe.

Not being able to convert past object is a known issue that they haven't solved just yet. microsoft/TypeScript#21732

Essentially though, yes, you've run into the issue with typing an untyped boundary. There is no simple way to do this unfortunately. There are some libraries to help generate validation functions from type definitions, but there's no perfect solution.

@maletor
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maletor commented Aug 15, 2020

I'll give 'runtypes' a try but it seems like #21732 may be close after a hard long two years.

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enhancement New feature or request good first issue Good for newcomers has pr there is a PR raised to close this package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin
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